OMAP3: PM: Fix the MMU on sequence in the asm code

Add necessary barriers after enabling MMU. Also use the sane way to
load pc and jump to it instead of executing ldma first up.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>