OMAP3: overo: add command support for mtd and ubi

The NAND linux partition format default was changed from jffs2 to ubi in
254973e6df0e48f1a72b67905185c774dcd9f394 but the corresponding commands were
not enabled.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
OMAP3: overo: increase linux partition to 8 MiB

Linux kernel at version 3.5 is about 3.5 MiB; test kernels for 3.10 exceed 4
MiB.  Prepare for future upgrades by increasing the NAND partition now.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>