drm/i915/huc: only load HuC on GTs that have VCS engines

On MTL the primary GT doesn't have any media capabilities, so no video
engines and no HuC. We must therefore skip the HuC fetch and load on
that specific case. Given that other multi-GT platforms might have HuC
on the primary GT, we can't just check for that and it is easier to
instead check for the lack of VCS engines.

Based on code from Aravind Iddamsetty

v2: clarify which engine_mask is used for each GT and why (Tvrtko)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Cc: John Harrison <john.c.harrison@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221108020600.3575467-1-daniele.ceraolospurio@intel.com