libdrm: add missing caps from kernel to drm.h

This just moves over some missing caps from the kernel.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

include/drm/drm.h

@@ -776,6 +776,8 @@ struct drm_event_vblank {
 
 #define DRM_CAP_DUMB_BUFFER 0x1
 #define DRM_CAP_VBLANK_HIGH_CRTC   0x2
+#define DRM_CAP_DUMB_PREFERRED_DEPTH 0x3
+#define DRM_CAP_DUMB_PREFER_SHADOW 0x4
 
 /* typedef area */
 typedef struct drm_clip_rect drm_clip_rect_t;