ARM: 7952/1: mm: Fix the memblock allocation for LPAE machines

Commit ad6492b8 added much needed memblock_virt_alloc_low() and further
commit 07bacb38 {memblock, bootmem: restore goal for alloc_low} fixed
the issue with low memory limit thanks to Yinghai. But even after all
these fixes, there is still one case where the limit check done with
ARCH_LOW_ADDRESS_LIMIT for low memory fails. Russell pointed out the
issue with 32 bit LPAE machines in below thread.
	https://lkml.org/lkml/2014/1/28/364



Since on some LPAE machines where memory start address is beyond 4GB,
the low memory marker in memblock will be set to default
ARCH_LOW_ADDRESS_LIMIT which is wrong. We can fix this by letting
architectures set the ARCH_LOW_ADDRESS_LIMIT using another export
similar to memblock_set_current_limit() but am not sure whether
its worth the trouble. Tell me if you think otherwise.

Rather am just trying to fix that one broken case using
memblock_virt_alloc() in setup code since the memblock.current_limit
is updated appropriately makes it work on all ARM 32 bit machines.

Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Strashko, Grygorii <grygorii.strashko@ti.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>