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>
diff --git a/drivers/gpu/drm/r128/r128_drv.h b/drivers/gpu/drm/r128/r128_drv.h
index 930c71b..56eb5e3 100644
--- a/drivers/gpu/drm/r128/r128_drv.h
+++ b/drivers/gpu/drm/r128/r128_drv.h
@@ -131,7 +131,7 @@
 	drm_r128_freelist_t *list_entry;
 } drm_r128_buf_priv_t;
 
-extern struct drm_ioctl_desc r128_ioctls[];
+extern const struct drm_ioctl_desc r128_ioctls[];
 extern int r128_max_ioctl;
 
 				/* r128_cce.c */