drm/amdkfd: Allocate gtt_sa_bitmap in long units

gtt_sa_bitmap is accessed by bitmap functions, which operate on longs.
Therefore the array should be allocated in long units. Also round up
in case the number of bits is not a multiple of BITS_PER_LONG.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>