board: Add Bananapi M1 support

Add initial support for bananapi M1 board with below features:
- U-Boot 2017.09
- Linux 4.13.7
- Default packages from buildroot

Cc: Jason <manager@sinovoip.com.cn>
Cc: hailymei@banana-pi.com <hailymei@banana-pi.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/bananapi/bananapi-m1/boot.cmd

@@ -0,0 +1,7 @@
+setenv bootargs console=ttyS0,115200 earlyprintk root=/dev/mmcblk0p2 rootwait
+
+mmc dev 0
+fatload mmc 0 $kernel_addr_r zImage
+fatload mmc 0 $fdt_addr_r sun7i-a20-bananapi.dts
+
+bootz $kernel_addr_r - $fdt_addr_r

board/bananapi/bananapi-m1/genimage.cfg

@@ -0,0 +1,33 @@
+image boot.vfat {
+	vfat {
+		files = {
+			"zImage",
+			"sun7i-a20-bananapi.dtb",
+			"boot.scr"
+		}
+	}
+	size = 64M
+}
+
+image sdcard.img {
+	hdimage {
+	}
+
+	partition u-boot {
+		in-partition-table = "no"
+		image = "u-boot-sunxi-with-spl.bin"
+		offset = 8192
+		size = 1040384 # 1MB - 8192
+	}
+
+	partition boot {
+		partition-type = 0xC
+		bootable = "true"
+		image = "boot.vfat"
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+	}
+}

board/bananapi/bananapi-m1/readme.txt

@@ -0,0 +1,37 @@
+Intro
+=====
+
+This default configuration will allow you to start experimenting with the
+buildroot environment for the Bananapi M1. With the current configuration
+it will bring-up the board, and allow access through the serial console.
+
+Bananapi M1 link:
+http://www.banana-pi.org/m1.html
+
+Wiki link:
+https://openedev.amarulasolutions.com/display/ODWIKI/Bananapi+M1
+
+This configuration uses U-Boot mainline and kernel mainline.
+
+How to build
+============
+
+    $ make bananapi_m1_defconfig
+    $ make
+
+Note: you will need access to the internet to download the required
+sources.
+
+How to write the SD card
+========================
+
+Once the build process is finished you will have an image called "sdcard.img"
+in the output/images/ directory.
+
+Copy the bootable "sdcard.img" onto an SD card with "dd":
+
+  $ sudo dd if=output/images/sdcard.img of=/dev/sdX
+  $ sudo sync
+
+Insert the micro SDcard in your Bananapi M1 and power it up. The console
+is on the serial line, 115200 8N1.