Exporting DRM_PRIME fd to VASurface requires direct
invocation of VA api VACreateSurface with
VASurfaceAttribExternalBufferDescriptor and other
necessary surface attributes.
https://bugzilla.gnome.org/show_bug.cgi?id=794817
Implements msdk frame allocator which is required from the driver.
Also makes these functions global so that GstMsdkAllocator could use
the allocated video memory later and couple with GstMsdkMemory.
GstMsdkContext keeps allocation information such as mfxFrameAllocRequest
and mfxFrameAllocResponse after allocation.
https://bugzilla.gnome.org/show_bug.cgi?id=790752