drm/i915/guc: New GuC scratch registers for Gen11

Gen11 adds new set of scratch registers that can be used for MMIO
based Host-to-Guc communication. Due to limited number of these
registers it is expected that host will use them only for command
transport buffers (CTB) communication setup if one is available.

Bspec: 21044

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190527183613.17076-10-michal.wajdeczko@intel.com