gfxstream: GrallocMinigbm uses platform_virtgpu

This removes the open-coding of virtgpu_drm access
and uses the platform_virtgpu layer.

Reviewed-by: Aaron Ruby <aruby@blackberry.com>
Acked-by: Yonggang Luo <luoyonggang@gmail.com>
Acked-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27246>

src/gfxstream/guest/android/GrallocEmulated.h

@@ -65,7 +65,7 @@ class EmulatedAHardwareBuffer {
 
 class EmulatedGralloc : public Gralloc {
    public:
-    EmulatedGralloc(VirtGpuDevice* device);
+    EmulatedGralloc(int32_t descriptor);
     ~EmulatedGralloc();
 
     GrallocType getGrallocType() override;
@@ -102,7 +102,7 @@ class EmulatedGralloc : public Gralloc {
     int getId(const AHardwareBuffer* ahb, uint64_t* id) override;
 
    private:
-    VirtGpuDevice* mDevice;
+    std::unique_ptr<VirtGpuDevice> mDevice;
     std::vector<std::unique_ptr<EmulatedAHardwareBuffer>> mOwned;
 };