ARM: OMAP4: Move the barrier memboclk_steal() as part of reserve callback

arm_memblock_steal() is not suppose to be used outside ->reserve callback.
OMAP barrier errata code was using it outside reserve callback and hence
it was broken.

Move the allocation as part of ->reserve callback to fix the it.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>