drm/i915: WaPsdDispatchEnable seems to be another name for WaDisablePSDDualDispatchEnable

The w/a database lists both WaPsdDispatchEnable and
WaDisablePSDDualDispatchEnable for VLV. They appear to be the same
thing, so list both names.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>