drm/msm: use PAGE_ALIGNED instead of IS_ALIGNED(PAGE_SIZE)

use mm.h definition

Cc: David Airlie <airlied@linux.ie>
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Rob Clark <robdclark@gmail.com>