drm/i915/huc: Add fetch support for gsc-loaded HuC binary

On newer platforms (starting DG2 G10 B-step and G11 A-step), ownership of
HuC loading has been moved from the GuC to the GSC. As part of the
change, the header format of the HuC binary has been updated and does not
match the GuC anymore. The GSC will perform all the required checks on
the binary size, so we only need to check that the version matches.

Note that since we still haven't added any gsc-loaded FWs, the
loaded_via_gsc variable will always be kept to its initialization value
of zero.

v2: Add a note about loaded_via_gsc being zero (Alan)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504204816.2082588-3-daniele.ceraolospurio@intel.com