drm/i915/mtl/huc: Use the media gt for the HuC getparam

On MTL, for obvious reasons, HuC is only available on the media tile.
We already disable SW support for HuC on the root gt due to the
absence of VCS engines, but we also need to update the getparam to point
to the HuC struct in the media GT.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230531235415.1467475-7-daniele.ceraolospurio@intel.com