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/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 71727b6..8f3dee0 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -907,6 +907,9 @@
 
 	/* whether async page flip is supported or not */
 	bool async_page_flip;
+
+	/* cursor size */
+	uint32_t cursor_width, cursor_height;
 };
 
 #define obj_to_crtc(x) container_of(x, struct drm_crtc, base)