kgsl: switch back to allocating from highmem

Commit 344c3acd switched kgsl to allocating
from highmem in page-sized chunks.  While this reduced pressure on highmem, it
may have increased pressure on lowmem to the point where lowmemorykiller
activity due to GFP_KERNEL requests rose.

b/19236185 Phone runs for about day, then apps start getting constantly killed
	   by lowmemorykiller

Change-Id: I92e82cc668cd10d8845d12e7c1bad6d980bc3956
Signed-off-by: Iliyan Malchev <malchev@google.com>