drm/xe: Allocate PF queue size on pow2 boundary

CIRC_SPACE does not work unless the size argument is a power of 2,
allocate PF queue size on power of 2 boundary.

Cc: stable@vger.kernel.org
Fixes: 3338e4f9 ("drm/xe: Use topology to determine page fault queue size")
Fixes: 29582e0e ("drm/xe: Add page queue multiplier")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://lore.kernel.org/r/20250702213511.3226167-1-matthew.brost@intel.com