configure: Require bit_depth field for VAAPI VP9 decode hwaccel

libva versions from 1.6.0 to 1.6.2 do not include it, and therefore
cannot work with VP9 profile >= 2.

Fixes ticket #6003.

configure

@@ -2689,7 +2689,7 @@ vp9_dxva2_hwaccel_deps="dxva2 DXVA_PicParams_VP9"
 vp9_dxva2_hwaccel_select="vp9_decoder"
 vp9_mediacodec_decoder_deps="mediacodec"
 vp9_mediacodec_hwaccel_deps="mediacodec"
-vp9_vaapi_hwaccel_deps="vaapi VADecPictureParameterBufferVP9"
+vp9_vaapi_hwaccel_deps="vaapi VADecPictureParameterBufferVP9_bit_depth"
 vp9_vaapi_hwaccel_select="vp9_decoder"
 wmv3_crystalhd_decoder_select="crystalhd"
 wmv3_d3d11va_hwaccel_select="vc1_d3d11va_hwaccel"
@@ -5610,7 +5610,7 @@ check_type "windows.h d3d11.h" "ID3D11VideoContext"
 check_type "d3d9.h dxva2api.h" DXVA2_ConfigPictureDecode -D_WIN32_WINNT=0x0602
 
 check_type "va/va.h" "VAPictureParameterBufferHEVC"
-check_type "va/va.h" "VADecPictureParameterBufferVP9"
+check_struct "va/va.h" "VADecPictureParameterBufferVP9" bit_depth
 check_type "va/va.h va/va_vpp.h" "VAProcPipelineParameterBuffer"
 check_type "va/va.h va/va_enc_h264.h" "VAEncPictureParameterBufferH264"
 check_type "va/va.h va/va_enc_hevc.h" "VAEncPictureParameterBufferHEVC"