New board: SolidRun ClearFog Base

My goal was to rely on upstreamed features as much as possible, which
means that some bits are only half-baked for now:

- Due to the DTS restructuring in upstream kernel, we require 4.11+. The
latest LTS or CIP kernels do not know about the -Base model.

- Linux has no generic support for SFP cages (yet). It seems that this
has hit the net-next tree in August 2017, but there's been no release
(it's probably targettting 4.14). Also, the merge only included the
required infrastructure; the mvneta driver conversion is not included.
Patches which finalize this exist in Russel King's tree and also in
random vendor trees.

- There's no access to the SPI flash in these versions of
uboot/linux/dts.

Signed-off-by: Jan Kundrát <jan.kundrat@cesnet.cz>
[Arnout:
 - rename to solidrun_clearfog_defconfig;
 - specify kernel headers version (default is now 4.15);
 - remove ext2 fs size override, the 4 extra MB are not needed;
 - U-Boot needs dtc and openssl;
 - add comments to defconfig;
 - update .gitlab-ci.yml;
 - mention in readme.txt that SFP support is missing;
 - add Jan to DEVELOPERS.
]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

board/solidrun/clearfog/boot.scr.txt

@@ -0,0 +1,5 @@
+setenv fdtfile armada-388-clearfog-base.dtb
+setenv bootargs root=/dev/mmcblk0p1
+load ${devtype} ${devnum}:${distro_bootpart} ${fdt_addr_r} ${prefix}/${fdtfile}
+load ${devtype} ${devnum}:${distro_bootpart} ${kernel_addr_r} ${prefix}/zImage
+bootz ${kernel_addr_r} - ${fdt_addr_r}

board/solidrun/clearfog/genimage.cfg

@@ -0,0 +1,16 @@
+image sdcard.img {
+	hdimage {
+	}
+
+	partition u-boot {
+		in-partition-table = "no"
+		image = "u-boot-spl.kwb"
+		offset = 512
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+		offset = 1M
+	}
+}

board/solidrun/clearfog/linux.fragment

@@ -0,0 +1 @@
+CONFIG_SENSORS_MCP3021=y

board/solidrun/clearfog/post-build.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+install -m 0644 -D $BINARIES_DIR/boot.scr $TARGET_DIR/boot/boot.scr

board/solidrun/clearfog/readme.txt

@@ -0,0 +1,68 @@
+**********************
+SolidRun Clearfog Base
+**********************
+
+This file documents Buildroot's support for the Clearfog Base by Solid Run.
+
+Vendor's documentation:
+https://wiki.solid-run.com/doku.php?id=products:a38x:documents
+
+Warning for eMMC variant of the MicroSoM
+========================================
+
+If you bought a MicroSoM version that includes an on-board eMMC flash, the
+built-in microSD card slot *WILL NOT WORK*. The Internet says that you have to
+upload the first bootloader via UART. This manual does not cover these steps;
+only MicroSoMs without the eMMC are supported.
+
+Limitations
+===========
+
+There's no access to the SPI flash in this combination of kernel/uboot/dts.
+
+There is no support for the SFP.
+
+Build
+=====
+
+Start with the default Buildroot's configuration for Clearfog:
+
+  make solidrun_clearfog_defconfig
+
+Build all components:
+
+  make
+
+The results of the build are available in ./output/images.
+
+Create a bootable SD card
+=========================
+
+To determine the device associated to the SD card have a look in the
+/proc/partitions file:
+
+  cat /proc/partitions
+
+Buildroot prepares a bootable "sdcard.img" image in the output/images/
+directory, ready to be dumped on a microSD card. Launch the following
+command as root:
+
+  dd if=./output/images/sdcard.img of=/dev/<your-microsd-device>
+
+*** WARNING! The script will destroy all the card content. Use with care! ***
+
+For details about the medium image layout, see the definition in
+board/solidrun/clearfog/genimage.cfg.
+
+Boot the Clearfog board
+=======================
+
+Here's how to boot the board:
+
+- Set up the DIP switches for microSD boot. The correct values are:
+  1: off, 2: off, 3: ON, 4: ON, 5: ON. In this scheme, switch #1" is closer to
+  the ethernet ports and #5 is closer to the microSD card, "ON" means towards
+  the SOM, and "off" means towards the SFP cage.
+- Connect to the board's console over the microUSB port.
+- Insert the SD card into the slot on the board (pins up).
+- Power up the board.