drm/xe/gsc: Define GSC FW for MTL

We track GSC FW based on its compatibility version, which is what
determines the interface it supports.
Also add a modparam override like the ones for GuC and HuC.

v2: fix module param description (John)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>