drm/radeon/kms: implement bo busy check + current domain

This implements the busy ioctl along with a current domain check.
returns 0 or -EBUSY
puts the current domain no matter what the answer.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/radeon_drm.h b/include/drm/radeon_drm.h
index af4b482..f81c323 100644
--- a/include/drm/radeon_drm.h
+++ b/include/drm/radeon_drm.h
@@ -838,7 +838,7 @@
 
 struct drm_radeon_gem_busy {
 	uint32_t	handle;
-	uint32_t	busy;
+	uint32_t        domain;
 };
 
 struct drm_radeon_gem_pread {