mei: gsc: retrieve the firmware version

Add a hook to retrieve the firmware version of the
GSC devices to bus-fixup.
GSC has a different MKHI clients GUIDs but the same message structure
to retrieve the firmware version as MEI so mei_fwver() can be reused.

CC: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419193314.526966-6-daniele.ceraolospurio@intel.com