drm/i915/gt: Add delay to let engine resumes properly

Sometimes engine reset fails because the engine resumes from an
incorrect RING_HEAD. Engine head failed to set to zero even after
writing into it. This is a timing issue and we experimented
different values and found out that 20ms delay works best based
on testing.

So, add a 20ms delay to let engine resumes from correct RING_HEAD.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13968


Signed-off-by: Nitin Gote <nitin.r.gote@intel.com>
Reviewed-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Link: https://lore.kernel.org/r/20250416103640.212269-1-nitin.r.gote@intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>