ENGR00297869: Image authentication is slow in u-boot-2013.04

authenticate_image() is slower than necessary since caching is not
enabled for OCRAM and Boot ROM. This patch turns them on.

It also sets the pu_irom_mmu_enabled bit in OCRAM so that ROM code
will properly flush caches.

Signed-off-by: Jay Monkman <jay.monkman@freescale.com>
(cherry picked from commit 9d3bd9da11fd7f35d818fe8d8c15c2906175df19)