drm/i915/mtl: Define GSC Proxy component interface

GSC Proxy component is used for communication between the
Intel graphics driver and MEI driver.

Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230502163854.317653-2-daniele.ceraolospurio@intel.com