drm/i915: Do not attempt to load the GSC multiple times

If the GSC FW fails to load the GSC HW hangs permanently; the only ways
to recover it are FLR or D3cold entry, with the former only being
supported on driver unload and the latter only on DGFX, for which we
don't need to load the GSC. Therefore, if GSC fails to load there is no
need to try again because the HW is stuck in the error state and the
submission to load the FW would just hang the GSCCS.

Note that, due to wa_14015076503, on MTL the GuC escalates all GSCCS
hangs to full GT resets, which would trigger a new attempt to load the
GSC FW in the post-reset HW re-init; this issue is also fixed by not
attempting to load the GSC FW after an error.

Fixes: 15bd4a67 ("drm/i915/gsc: GSC firmware loading")
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: 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: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v6.3+
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240820215952.2290807-1-daniele.ceraolospurio@intel.com