drm/i915: Convert i915_gem_object_ops->flags values to use BIT()

Having just watched someone add a new value, 0x3, without realising that
the flags were bit values, I have come to appreciate the value in using
BIT.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170523103116.32239-1-chris@chris-wilson.co.ukReviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_gem_object.h

@@ -37,8 +37,8 @@
 
 struct drm_i915_gem_object_ops {
 	unsigned int flags;
-#define I915_GEM_OBJECT_HAS_STRUCT_PAGE 0x1
-#define I915_GEM_OBJECT_IS_SHRINKABLE   0x2
+#define I915_GEM_OBJECT_HAS_STRUCT_PAGE BIT(0)
+#define I915_GEM_OBJECT_IS_SHRINKABLE   BIT(1)
 
 	/* Interface between the GEM object and its backing storage.
 	 * get_pages() is called once prior to the use of the associated set