drm/i915/gsc: implement wa 14015076503

The WA states that we need to alert the GSC FW before doing a GSC engine
reset and then wait for 200ms. The GuC owns engine reset, so on the i915
side we only need to apply this for full GT reset.

Given that we do full GT resets in the resume paths to cleanup the HW
state and that a long wait in those scenarios would not be acceptable,
a faster path has been introduced where, if the GSC is idle, we try first
to individually reset the GuC and all engines except the GSC and only fall
back to full reset if that fails.

Note: according to the WA specs, if the GSC is idle it should be possible
to only wait for the uC wakeup time (~15ms) instead of the whole 200ms.
However, the GSC FW team have mentioned that the wakeup time can change
based on other things going on in the HW and pcode, so a good security
margin would be required. Given that when the GSC is idle we already
skip the wait & reset entirely and that this reduced wait would still
likely be too long to use in resume paths, it's not worth adding support
for this reduced wait.

v2: add comment to explain why it is safe to skip the GSC reset (John)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: John Harrison <john.c.harrison@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323231857.2194435-2-daniele.ceraolospurio@intel.com