Revert "remove function find_mtd_part() from /lib/functions.sh"

Reverting commit 34641.
Function find_mtd_part() is needed by some scripts deployed
for certain targets but not including boot.sh after all.
Still, all this certainly needs some love.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34642 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/base-files/files/lib/functions.sh

@@ -220,6 +220,15 @@ include() {
 	done
 }
 
+find_mtd_part() {
+	local PART="$(grep "\"$1\"" /proc/mtd | awk -F: '{print $1}')"
+	local PREFIX=/dev/mtdblock
+
+	PART="${PART##mtd}"
+	[ -d /dev/mtdblock ] && PREFIX=/dev/mtdblock/
+	echo "${PART:+$PREFIX$PART}"
+}
+
 strtok() { # <string> { <variable> [<separator>] ... }
 	local tmp
 	local val="$1"