- qsv_internal.h: Remove unnecessary include va_drm.h
- qsv_internal.h: Enable AVCODEC_QSV_LINUX_SESSION_HANDLE on Linux/VA only
- hwcontext_qsv.c: Do not allow child_device_type VAAPI for Windows until
  support is added, keep D3D11/DXVA2 as more prioritary defaults.

Initial review at https://github.com/intel-media-ci/ffmpeg/pull/619/Signed-off-by: Sil Vilerino <sivileri@microsoft.com>
Reviewed-by: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Reviewed-by: Wu, Tong1 <tong1.wu@intel.com>