brcm2708: Implement sysupgrade

Implement sysupgrade for Raspberry Pi, similar to the way it is done on x86:
The config files are saved in the boot partition and moved to where they are
normally expected in preinit.

Also add optional gzip compression for the SD card image, since this can save
a lot of space (76M vs 6M), also similar to x86.

Signed-off-by: Bruno Randolf <br1@einfach.org>

SVN-Revision: 46347

target/linux/brcm2708/base-files/lib/preinit/79_move_config

@@ -0,0 +1,18 @@
+#!/bin/sh
+# Copyright (C) 2015 OpenWrt.org
+
+BOOTPART=/dev/mmcblk0p1
+
+move_config() {
+	if [ -b $BOOTPART ]; then
+		insmod nls_cp437
+		insmod nls_iso8859-1
+		insmod fat
+		insmod vfat
+		mount -t vfat -o rw,noatime $BOOTPART /mnt
+		[ -f /mnt/sysupgrade.tgz ] && mv -f /mnt/sysupgrade.tgz /
+		umount /mnt
+	fi
+}
+
+boot_hook_add preinit_mount_root move_config