board: Add support for Engicam Is.IoT MX6UL SOM

Add initial support for Engicam Is.IoT MX6UL SOM board
with below features:
- U-Boot 2017.07-rc1
- Linux 4.11.5
- Default packages from buildroot

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
[Thomas: add host-dosfstools/host-mtools.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/engicam/isiot/genimage.cfg

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+image boot.vfat {
+	vfat {
+		files = {
+			"uImage",
+			"imx6ul-isiot-emmc.dtb"
+		}
+	}
+	size = 64M
+}
+
+image sdcard.img {
+	hdimage {
+	}
+
+	partition SPL {
+		in-partition-table = "no"
+		image = "SPL"
+		offset = 1024
+	}
+
+	partition u-boot-dtb {
+		in-partition-table = "no"
+		image = "u-boot-dtb.img"
+		offset = 69K
+	}
+
+	partition boot {
+		partition-type = 0xC
+		bootable = "true"
+		image = "boot.vfat"
+		offset = 8M
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext2"
+	}
+}

board/engicam/isiot/readme.txt

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+********************************************
+Buildroot for Engicam Is.IoT SOM platforms:
+********************************************
+
+This file documents the Buildroot support for all Engicam Is.IoT MX6UL
+SOM platform boards.
+
+Is.IoT MX6UL SOM Starter kits:
+https://www.engicam.com/vis-prod/101122
+
+This configuration uses U-Boot mainline and kernel mainline.
+
+Build
+=====
+
+First, configure Buildroot for the Engicam Is.IoT MX6UL SOM:
+
+- for Is.IoT MX6UL SOM:
+
+  make engicam_imx6ul_isiot_defconfig
+
+Build all components:
+
+  make
+
+You will find the following files in output/images/:
+  - imx6ul-isiot-emmc.dtb
+  - rootfs.ext4
+  - rootfs.tar
+  - sdcard.img
+  - SPL
+  - u-boot-dtb.img
+  - uImage
+
+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 SD card. Launch the following
+command as root:
+
+  dd if=output/images/sdcard.img of=/dev/<your-sd-device>
+  sync
+
+*** WARNING! This will destroy all the card content. Use with care! ***
+
+For details about the medium image layout, see the definition in
+board/engicam/isiot/genimage.cfg
+
+Boot the Is.IoT MX6UL boards with SD boot:
+=========================================
+
+To boot your newly created system:
+- insert the SD card in the SD slot of the board;
+- connect 3-wire RS232 serial port J28 on board, and connect with other
+  serial end or USB cable(if serial-to-usb converter used) using
+  a terminal emulator at 115200 bps, 8n1;
+- close JM3 for sd boot.
+- power on the board.
+
+Enjoy!