ramips: split base-files into subtargets

While most of the target's contents are split into subtargets, the
base-files are maintained for the target as a whole.

However, OpenWrt already implements a mechanism that will use (and
even prefer) files in the subtargets' directories. This can be
exploited to make several scripts subtarget-specific and thus save
some space.

In certain cases, keeping files in parent (=target) base-files was
more convenient, and thus no splitting was performed for those.

Note that this will increase overall code lines, but reduce code
per subtarget.

base-files ipk size reduction:
master (mt7621)   60958 B
split (mt7620)    46358 B (- 14.3 kiB)
split (mt7621)    48759 B (- 11.9 kiB)
split (mt76x8)    44948 B (- 15.6 kiB)
split (rt288x)    43508 B (- 17.0 kiB)
split (rt305x)    45616 B (- 15.0 kiB)
split (rt3883)    44176 B (- 16.4 kiB)

Run-tested on:
GL.iNet GL-MT300N-V2 (mt76x8)
D-Link DWR-116 (mt7620)

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/rt3883/base-files/lib/preinit/04_handle_checksumming

@@ -0,0 +1,32 @@
+#!/bin/sh
+
+# Netgear WNCE2001 has does a checksum check on boot and goes into recovery
+# tftp mode when the check fails.  Initializing the JFFS2 partition triggers
+# this, so we make sure to zero checksum and size to be checksummed before
+# that happens, so this needs to run very early during boot.
+
+do_checksumming_disable() {
+	. /lib/functions.sh
+
+	local board=$(board_name)
+
+	case "$board" in
+	asus,rt-n56u)
+		echo "Board is ASUS RT-N56U, replacing uImage header..."
+		local firmware_mtd=$(find_mtd_part firmware)
+		local rootfs_mtd=$(find_mtd_part rootfs)
+		local rootfs_data_mtd=$(find_mtd_part rootfs_data)
+		local rootfs_len=$(grep \"rootfs\" /proc/mtd | awk -F' ' '{print "0x"$2}')
+		local rootfs_data_len=$(grep \"rootfs_data\" /proc/mtd | awk -F' ' '{print "0x"$2}')
+		local offset=$(echo "$rootfs_len $rootfs_data_len 0x40" | awk -F' ' '{printf "%i",$1-$2-$3}')
+		local signature=$(dd if=$rootfs_mtd skip=$offset bs=1 count=4 2>/dev/null | hexdump -v -n 4 -e '1/1 "%02x"')
+		if [ "$signature" = "27051956" ]; then
+			dd conv=notrunc if=$rootfs_mtd skip=$offset of=$firmware_mtd bs=1 count=64 2>/dev/null
+		fi
+	;;
+	esac
+
+	return 0
+}
+
+boot_hook_add preinit_main do_checksumming_disable