drm: const'ify ioctls table (v2)

Because, there is no reason for it not to be const.

v1: original
v2: fix compile break in vmwgfx, and couple related cleanups suggested
    by Ville Syrjälä

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/qxl/qxl_drv.h

@@ -319,7 +319,7 @@ struct qxl_device {
 /* forward declaration for QXL_INFO_IO */
 void qxl_io_log(struct qxl_device *qdev, const char *fmt, ...);
 
-extern struct drm_ioctl_desc qxl_ioctls[];
+extern const struct drm_ioctl_desc qxl_ioctls[];
 extern int qxl_max_ioctl;
 
 int qxl_driver_load(struct drm_device *dev, unsigned long flags);