Implement GPU syncpoints (#980)

* Implement GPU syncpoints

This adds support for GPU syncpoints on the GPU backend & nvservices.

Everything that was implemented here is based on my researches,
hardware testing of the GM20B and reversing of nvservices (8.1.0).

Thanks to @fincs for the informations about some behaviours of the pusher
and for the initial informations about syncpoints.

* syncpoint: address gdkchan's comments

* Add some missing logic to handle SubmitGpfifo correctly

* Handle the NV event API correctly

* evnt => hostEvent

* Finish addressing gdkchan's comments

* nvservices: write the output buffer even when an error is returned

* dma pusher: Implemnet prefetch barrier

lso fix when the commands should be prefetch.

* Partially fix prefetch barrier

* Add a missing syncpoint check in QueryEvent of NvHostSyncPt

* Address Ac_K's comments and fix GetSyncpoint for ChannelResourcePolicy == Channel

* fix SyncptWait & SyncptWaitEx cmds logic

* Address ripinperi's comments

* Address gdkchan's comments

* Move user event management to the control channel

* Fix mm implementation, nvdec works again

* Address ripinperi's comments

* Address gdkchan's comments

* Implement nvhost-ctrl close accurately + make nvservices dispose channels when stopping the emulator

* Fix typo in MultiMediaOperationType

Ryujinx.Graphics.Gpu/ClassId.cs

@@ -9,6 +9,7 @@ namespace Ryujinx.Graphics.Gpu
         Engine3D            = 0xb197,
         EngineCompute       = 0xb1c0,
         EngineInline2Memory = 0xa140,
-        EngineDma           = 0xb0b5
+        EngineDma           = 0xb0b5,
+        EngineGpfifo        = 0xb06f
     }
 }