drm/xe/gsc: Parse GSC FW header

The GSC blob starts with a layout header, from which we can move to the
boot directory, which in turns allows us to find the CPD. The CPD uses
the same format as the one in the HuC binary, so we can re-use the same
parsing code to get to the manifest, which contains the release and
security versions of the FW.

v2: Fix comments in struct definition (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>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>