Add support for PREEMPT_RT kernels

Add a series of #ifdefs in gckOS_WaitSignal() to support RT kernels,
where the completion mechanism has been changed to use swait instead of
complex wait queues.

This is based on a patch previously provided to meta-fsl-arm by
Jacob Kroon:
Freescale/meta-freescale@5ebb4e1

In order to be able to load the RT version of the module, the kernel
itself must be patched to export the swait_prepare_locked() and
swait_finish_locked() functions.

Signed-off-by: Dominic Sacré <dominic.sacre@gmx.de>

kernel-module-imx-gpu-viv-src/hal/os/linux/kernel/gc_hal_kernel_os.c

@@ -7386,7 +7386,11 @@ gckOS_WaitSignal(
 
     might_sleep();
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+    raw_spin_lock_irq(&signal->obj.wait.lock);
+#else
     spin_lock_irq(&signal->obj.wait.lock);
+#endif
 
     if (signal->obj.done)
     {
@@ -7408,9 +7412,14 @@ gckOS_WaitSignal(
             ? MAX_SCHEDULE_TIMEOUT
             : Wait * HZ / 1000;
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+        DEFINE_SWAITER(wait);
+        swait_prepare_locked(&signal->obj.wait, &wait);
+#else
         DECLARE_WAITQUEUE(wait, current);
         wait.flags |= WQ_FLAG_EXCLUSIVE;
         __add_wait_queue_tail(&signal->obj.wait, &wait);
+#endif
 
         while (gcvTRUE)
         {
@@ -7422,9 +7431,15 @@ gckOS_WaitSignal(
             }
 
             __set_current_state(TASK_INTERRUPTIBLE);
+#ifdef CONFIG_PREEMPT_RT_BASE
+            raw_spin_unlock_irq(&signal->obj.wait.lock);
+            timeout = schedule_timeout(timeout);
+            raw_spin_lock_irq(&signal->obj.wait.lock);
+#else
             spin_unlock_irq(&signal->obj.wait.lock);
             timeout = schedule_timeout(timeout);
             spin_lock_irq(&signal->obj.wait.lock);
+#endif
 
             if (signal->obj.done)
             {
@@ -7445,10 +7460,18 @@ gckOS_WaitSignal(
             }
         }
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+        swait_finish_locked(&signal->obj.wait, &wait);
+#else
         __remove_wait_queue(&signal->obj.wait, &wait);
+#endif
     }
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+    raw_spin_unlock_irq(&signal->obj.wait.lock);
+#else
     spin_unlock_irq(&signal->obj.wait.lock);
+#endif
 
 OnError:
     /* Return status. */