drm/i915/guc: Enable PXP GuC autoteardown flow

This feature flag enables GuC autoteardown which allows for a grace
period before session teardown.

Also add a HAS_PXP() helper to share with the other place that wants
to check.

Signed-off-by: Juston Li <juston.li@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240906174038.1468026-1-John.C.Harrison@Intel.com