drm/i915: Assert that the exec object lookup table is a power-of-two

As we make the simplification of using a power-of-two size for the
execbuffer handle-to-object TLB, we should validate that this is actually
true and so clarify that premise.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -44,6 +44,7 @@ eb_create(int size)
 {
 	struct eb_objects *eb;
 	int count = PAGE_SIZE / sizeof(struct hlist_head) / 2;
+	BUILD_BUG_ON(!is_power_of_2(PAGE_SIZE / sizeof(struct hlist_head)));
 	while (count > size)
 		count >>= 1;
 	eb = kzalloc(count*sizeof(struct hlist_head) +