Merge from bittboy/buildroot@db180c0

board/friendlyarm/nanopi-m4/extlinux.conf

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+label NanoPi M4 5.1-rc1
+  kernel /boot/Image
+  devicetree /boot/rk3399-nanopi-m4.dtb
+  append earlycon=uart8250,mmio32,0xff1a0000 root=/dev/mmcblk1p1 rootwait

board/friendlyarm/nanopi-m4/genimage.cfg

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+image sdcard.img {
+	hdimage {
+	}
+
+	partition u-boot-spl-dtb {
+		in-partition-table = "no"
+		image = "u-boot-spl-dtb.img"
+		offset = 32K
+	}
+
+	partition u-boot-dtb {
+		in-partition-table = "no"
+		image = "u-boot.itb"
+		offset = 8M
+		size = 30M
+	}
+
+	partition rootfs {
+		partition-type = 0x83
+		image = "rootfs.ext4"
+	}
+}

board/friendlyarm/nanopi-m4/post-build.sh

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+#!/bin/sh
+
+MKIMAGE=$HOST_DIR/bin/mkimage
+BOARD_DIR="$(dirname $0)"
+
+$MKIMAGE -n rk3399 -T rksd -d $BINARIES_DIR/u-boot-spl-dtb.bin $BINARIES_DIR/u-boot-spl-dtb.img
+
+install -m 0644 -D $BOARD_DIR/extlinux.conf $TARGET_DIR/boot/extlinux/extlinux.conf

board/friendlyarm/nanopi-m4/readme.txt

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+Intro
+=====
+
+NanoPi M4 is a RK3399 SoC based ARM board.
+
+Wiki: https://wiki.amarulasolutions.com/bsp/rockchip/rk3399/nanopi_m4.html
+
+Build
+=====
+
+Run NanoPi M4 configuration
+
+  $ make nanopi_m4_defconfig
+
+To build, run make command.
+
+  $ make
+
+Files created in output directory
+=================================
+output/images/
+├── bl31.bin
+├── Image
+├── rk3399-nanopi-m4.dtb
+├── rootfs.ext2
+├── rootfs.ext4 -> rootfs.ext2
+├── rootfs.tar
+├── sdcard.img
+├── u-boot.bin
+├── u-boot.itb
+├── u-boot-spl-dtb.bin
+└── u-boot-spl-dtb.img
+
+Creating bootable SD card:
+=========================
+
+Simply invoke (as root)
+
+  # dd if=output/images/sdcard.img of=/dev/sdX && sync
+
+Where X is your SD card device
+
+Serial console
+--------------
+Baudrate for this board is 1500000