drm/i915: Assert that created vma has a whole number of pages

VMA (and their objects) are supposed to composed of whole pages. Add an
assert to catch any invalid construct when we create the VMA.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170119192659.31789-6-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_vma.c

@@ -110,6 +110,8 @@ vma_create(struct drm_i915_gem_object *obj,
 	if (unlikely(vma->size > vm->total))
 		goto err_vma;
 
+	GEM_BUG_ON(!IS_ALIGNED(vma->size, I915_GTT_PAGE_SIZE));
+
 	if (i915_is_ggtt(vm)) {
 		if (unlikely(overflows_type(vma->size, u32)))
 			goto err_vma;