ath79: 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 (especially helpful for the tiny devices).

The only script remaining in parent base-files is
/etc/hotplug.d/ieee80211/00-wifi-migration, everything else is
moved/split.

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

base-files ipk size reduction:
master (generic)   49135 B
split (generic)    48533 B (- 0.6 kiB)
split (tiny)       43337 B (- 5.7 kiB)
split (nand)       44423 B (- 4.6 kiB)

Tested on TL-WR1043ND v4 (generic) and TL-WR841N v12 (tiny).

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

target/linux/ath79/tiny/base-files/lib/upgrade/platform.sh

@@ -0,0 +1,20 @@
+#
+# Copyright (C) 2011 OpenWrt.org
+#
+
+PART_NAME=firmware
+REQUIRE_IMAGE_METADATA=1
+
+platform_check_image() {
+	return 0
+}
+
+platform_do_upgrade() {
+	local board=$(board_name)
+
+	case "$board" in
+	*)
+		default_do_upgrade "$1"
+		;;
+	esac
+}