drm/xe/guc_submit: Introduce pause/unpause() helpers for PF

drm/xe/guc_submit: Introduce pause/unpause() helpers for PF

Introduce pause/unpause() helpers which stop/start further runs of
submission tasks on given GuC and can be called from PF context. This
is in preparation of usecases where we simply need to stop/start the
scheduler without losing GuC state and don't require dealing with VF
migration.

v7: Reword commit message (Matthew Brost)

Signed-off-by: Raag Jadav <raag.jadav@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patch.msgid.link/20251030122357.128825-3-raag.jadav@intel.com