Add mknod support to init

Takes the following arguments:
mknod name, type[b/c/u/p], mode, major, minor

Based on implementation from:
https://gitorious.org/openaos-cyanogenmod/device_archos/commit/79da8a8

(cherry picked from commit 0f18f79da22639ac24e0d06e167fce7e71a39e3b)

Change-Id: Id7e512062913d9a99c3630ecc1a7138ab4bdb036