Blackfin: bf526-ezbrd: enable BootROM-OOB layout when booting from NAND

We need to use the Blackfin BootROM-specific OOB layout when we boot out
of NAND as that is what the on-chip ROM expects.

Also need to increase the monitor size a little to accommodate the extra
NAND code overhead.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>