Kernel: Implement basic VirGL device

This commit flips VirtIOGPU back to using a Mutex for its operation
lock (instead of a spinlock). This is necessary for avoiding a few
system hangs when queuing actions on the driver from multiple
processes, which becomes much more of an issue when using VirGL from
multiple userspace process.

This does result in a few code paths where we inevitably have to grab
a mutex from inside a spinlock, the only way to fix both issues is to
move to issuing asynchronous virtio gpu commands.

Kernel/CMakeLists.txt

@@ -86,6 +86,7 @@ set(KERNEL_SOURCES
     Graphics/VGA/PCIAdapter.cpp
     Graphics/VirtIOGPU/FramebufferDevice.cpp
     Graphics/VirtIOGPU/Console.cpp
+    Graphics/VirtIOGPU/GPU3DDevice.cpp
     Graphics/VirtIOGPU/GraphicsAdapter.cpp
     Graphics/GenericFramebufferDevice.cpp
     SanCov.cpp