drm: add DRM_CAPs for cursor size

Some hardware may not support standard 64x64 cursors.  Add
a drm cap to query the cursor size from the kernel.  Some examples
include radeon CIK parts (128x128 cursors) and armada (32x64 or 64x32).
This allows things like device specific ddxes to remove asics specific
logic and also allows xf86-video-modesetting to work properly with hw
cursors on this hardware. Default to 64 if the driver doesn't specify
a size.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index 3c9a833..b06c8ed 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -619,6 +619,8 @@
 #define  DRM_PRIME_CAP_EXPORT		0x2
 #define DRM_CAP_TIMESTAMP_MONOTONIC	0x6
 #define DRM_CAP_ASYNC_PAGE_FLIP		0x7
+#define DRM_CAP_CURSOR_WIDTH		0x8
+#define DRM_CAP_CURSOR_HEIGHT		0x9
 
 /** DRM_IOCTL_GET_CAP ioctl argument type */
 struct drm_get_cap {