drm/i915/gvt: grab runtime pm first for forcewake use

in workload_thread, it should grab runtime pm wakelock and later
uncore forcewake get will check rpm wakelock held successfully.
otherwise, sometimes, rpm wakelock not hold and print call trace below:

 Call Trace:
  intel_uncore_forcewake_get+0x15/0x20 [i915]
  workload_thread+0x5f9/0x16f0 [i915]
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to+0x85/0x3f0
  ? __switch_to_asm+0x40/0x70
  ? do_wait_intr_irq+0x90/0x90
  kthread+0x121/0x140
  ? intel_vgpu_clean_workloads+0x100/0x100 [i915]
  ? kthread_park+0x90/0x90
  ret_from_fork+0x35/0x40
 --[ end trace 86525f742a02e12c ]--

v2: adapted to use rpm structure.

Fixes: 251d46b0 ("drm/i915/gvt: Pin the per-engine GVT shadow contexts")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/scheduler.c

@@ -990,6 +990,7 @@ static int workload_thread(void *priv)
 	int ret;
 	bool need_force_wake = (INTEL_GEN(gvt->dev_priv) >= 9);
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	struct intel_runtime_pm *rpm = &gvt->dev_priv->runtime_pm;
 
 	kfree(p);
 
@@ -1013,6 +1014,8 @@ static int workload_thread(void *priv)
 				workload->ring_id, workload,
 				workload->vgpu->id);
 
+		intel_runtime_pm_get(rpm);
+
 		gvt_dbg_sched("ring id %d will dispatch workload %p\n",
 				workload->ring_id, workload);
 
@@ -1042,6 +1045,7 @@ static int workload_thread(void *priv)
 			intel_uncore_forcewake_put(&gvt->dev_priv->uncore,
 					FORCEWAKE_ALL);
 
+		intel_runtime_pm_put_unchecked(rpm);
 		if (ret && (vgpu_is_vm_unhealthy(ret)))
 			enter_failsafe_mode(vgpu, GVT_FAILSAFE_GUEST_ERR);
 	}