fs: migrate to nativesd

with aging nand storage filled with BBs, a crappy filesystem (namely yaffs2) and high speed sdcards these daysit really makes sense to mount /system and /data on the sdcard.
prerequisite is a fast sdcard (class 6, class 10 - they're really cheap these days).

transfer rates are ~2.5x-3x nand speed with a decent sdcard and we can benefit from ext4.

of course, one needs a compatible recovery (built with this change included) and a partitioned sdcard.
e.g. minitool with win and fdisk with *nix.

 * 1st primary sdcard partition: fat32 storage (as before)
 * 2nd primary sdcard partition: ext4 mounted to /system
 * 3rd primary sdcard partition: ext4 mounted to /data