sunxi: add sysupgrade support

Enalbe builtin support for FAT filesystem as we need to mount boot
partition to store sysupgrade.tgz there

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

target/linux/sunxi/base-files/lib/preinit/79_move_config

@@ -0,0 +1,20 @@
+#!/bin/sh
+# Copyright (C) 2012-2015 OpenWrt.org
+
+move_config() {
+	local partdev
+
+	. /lib/upgrade/common.sh
+
+	if export_bootdevice && export_partdevice partdev -1; then
+		if mount -t vfat -o rw,noatime "/dev/$partdev" /mnt; then
+			if [ -f /mnt/sysupgrade.tgz ]; then
+				mv -f /mnt/sysupgrade.tgz /
+			fi
+			umount /mnt
+		fi
+	fi
+}
+
+boot_hook_add preinit_mount_root move_config
+