drm/i915: limit double GT reset to pre-MTL

Commit 3db9d590 ("drm/i915/gt: Reset twice") modified the code to
always hit the GDRST register twice when doing a reset, with the
reported aim to fix invalid post-reset engine state on some platforms
(Jasperlake being the only one actually mentioned).

This is a problem on MTL, due to the fact that we have to apply a time
consuming WA (coming in the next patch) every time we hit the GDRST
register in a way that can include the GSC engine. Even post MTL, the
expectation is that we'll have some work to do before and after hitting
the GDRST if the GSC is involved.

Since the issue requiring the double reset seems to be limited to older
platforms, instead of trying to handle the double-reset on MTL and
future platforms it is just easier to turn it off. The default on MTL is
also for GuC to own engine reset, with i915 only covering full-GT reset.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323231857.2194435-1-daniele.ceraolospurio@intel.com