BeagleBoard X15: new board

This configuration provides a basic setup for using Buildroot
to create a sd-card image a BeagleBoard X15 board.

[Peter: use 512M ext4 partition, linux 4.9 and u-boot 2016.11]
Signed-off-by: Theo Debrouwere <Theo.Debrouwere@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/beagleboardx15/genimage.cfg

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+image boot.vfat {
+	vfat {
+		files = {
+			"MLO",
+			"u-boot.img"
+		}
+	}
+	size = 4M
+}
+
+image sdcard.img {
+	hdimage {
+	}
+
+	partition u-boot {
+		partition-type = 0xC
+		bootable = "true"
+                image = "boot.vfat"
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+		size = 512M
+	}
+}

board/beagleboardx15/post-image.sh

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+#!/bin/sh
+
+BOARD_DIR="$(dirname $0)"
+
+GENIMAGE_CFG="${BOARD_DIR}/genimage.cfg"
+GENIMAGE_TMP="${BUILD_DIR}/genimage.tmp"
+
+rm -rf "${GENIMAGE_TMP}"
+
+genimage \
+    --rootpath "${TARGET_DIR}" \
+    --tmppath "${GENIMAGE_TMP}" \
+    --inputpath "${BINARIES_DIR}" \
+    --outputpath "${BINARIES_DIR}" \
+    --config "${GENIMAGE_CFG}"

board/beagleboardx15/readme.txt

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+BeagleBoard X15
+
+Intro
+=====
+This config currently supports the beagleboard x15,
+and generates a barebone image.
+
+The image must be flashed to a SD card to be used.
+
+How to build it
+===============
+
+  $ make beagleboardx15_defconfig
+
+Then you can edit the build options using
+
+  $ make menuconfig
+
+Compile all and build a sdcard image:
+
+  $ make
+
+Result of the build
+-------------------
+
+After building, you should get a tree like this:
+
+  output/images/
+  ├── am57xx-beagle-x15.dtb
+  ├── am57xx-beagle-x15-revb1.dtb
+  ├── boot.vfat
+  ├── MLO
+  ├── rootfs.ext2
+  ├── rootfs.ext4
+  ├── rootfs.tar
+  ├── sdcard.img
+  ├── u-boot.img
+  ├── u-boot-spl.bin
+  └── zImage
+
+How to write the microSD 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

configs/beagleboardx15_defconfig

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+BR2_arm=y
+BR2_cortex_a15=y
+BR2_ROOTFS_POST_IMAGE_SCRIPT="board/beagleboardx15/post-image.sh"
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.9"
+BR2_LINUX_KERNEL_DEFCONFIG="omap2plus"
+BR2_LINUX_KERNEL_DTS_SUPPORT=y
+BR2_LINUX_KERNEL_INTREE_DTS_NAME="am57xx-beagle-x15 am57xx-beagle-x15-revb1"
+BR2_LINUX_KERNEL_INSTALL_TARGET=y
+BR2_TARGET_ROOTFS_EXT2=y
+BR2_TARGET_ROOTFS_EXT2_4=y
+BR2_TARGET_UBOOT=y
+BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
+BR2_TARGET_UBOOT_CUSTOM_VERSION=y
+BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2016.11"
+BR2_TARGET_UBOOT_BOARD_DEFCONFIG="am57xx_evm"
+BR2_TARGET_UBOOT_NEEDS_DTC=y
+# BR2_TARGET_UBOOT_FORMAT_BIN is not set
+BR2_TARGET_UBOOT_FORMAT_IMG=y
+BR2_TARGET_UBOOT_FORMAT_CUSTOM=y
+BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME="spl/u-boot-spl.bin"
+BR2_TARGET_UBOOT_SPL=y
+BR2_TARGET_UBOOT_SPL_NAME="MLO"
+BR2_PACKAGE_HOST_DOSFSTOOLS=y
+BR2_PACKAGE_HOST_GENIMAGE=y
+BR2_PACKAGE_HOST_MTOOLS=y