Avoid trying to invalidate the TLB in the middle of performing an
engine reset, as this may result in the reset timing out. Currently,
the TLB invalidate is only serialised by its own mutex, forgoing the
uncore lock, but we can take the uncore->lock as well to serialise
the mmio access, thereby serialising with the GDRST.

Tested on a NUC5i7RYB, BIOS RYBDWi35.86A.0380.2019.0517.1530 with
i915 selftest/hangcheck.

Cc: stable@vger.kernel.org  # v4.4 and upper
Fixes: 7938d615 ("drm/i915: Flush TLBs before releasing backing store")
Reported-by: NMauro Carvalho Chehab <mchehab@kernel.org>
Tested-by: NMauro Carvalho Chehab <mchehab@kernel.org>
Reviewed-by: NMauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: NChris Wilson <chris.p.wilson@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: NAndi Shyti <andi.shyti@linux.intel.com>
Acked-by: NThomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1e59a7c45dd919a530256b9ac721ac6ea86c0677.1657639152.git.mchehab@kernel.org