drm/i915/mtl: add GSC CS reset support

The GSC CS has its own dedicated bit in the GDRST register.

Bspec: 52549
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221102171047.2787951-5-daniele.ceraolospurio@intel.com