drm/i915/guc: Grab RPM wakelock while disabling GuC interrupts

Disabling GuC interrupts involves access to GuC IRQ control registers
hence ensure device is RPM awake.

v1-v2: old changelog
1: Add comment about need to synchronize flush work and log runtime
   destroy
2: Moved patch earlier in the series and removed comment about future
work. (Tvrtko)

v3: Added assert_rpm_wakelock_held() to gen9_*_guc_interrupts. (Chris)

Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1516808821-3638-1-git-send-email-sagar.a.kamble@intel.com