The ring scratch pages don't have a PPGTT mapping, so the DERRM SRM
should target the global GTT instead.

v2: Add MI_SRM_LRM_GLOBAL_GTT define for -fixes
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>