When using GPU surfaces with QSV, one needs to supply a frame allocator,
which will be invoked to pass surface pools to libmfx.
For encoding, this allocator gets invoked not only for the pool of input
frames, but also for a separate pool of (apparently) reconstructed frames
and another pool of MFX_FOURCC_P8, which on Windows needs to return
D3DFMT_P8 D3D surfaces. Those are probably used to store the encoded
bitstream on the GPU.
Signed-off-by: Maxym Dmytrychenko <maxym.dmytrychenko@intel.com>