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/gma500/psb_drv.c

@@ -131,7 +131,7 @@ static int psb_gamma_ioctl(struct drm_device *dev, void *data,
 static int psb_dpst_bl_ioctl(struct drm_device *dev, void *data,
 			     struct drm_file *file_priv);
 
-static struct drm_ioctl_desc psb_ioctls[] = {
+static const struct drm_ioctl_desc psb_ioctls[] = {
 	DRM_IOCTL_DEF_DRV(GMA_ADB, psb_adb_ioctl, DRM_AUTH),
 	DRM_IOCTL_DEF_DRV(GMA_MODE_OPERATION, psb_mode_operation_ioctl,
 		      DRM_AUTH),