msdkvpp: allow BGRx in DMABuf mode in the src pad

Tested with the pipeline below:

gst-launch-1.0 videotestsrc ! msdkvpp ! \
video/x-raw\(memory:DMABuf\),format=BGRx ! glimagesink

sys/msdk/gstmsdkvpp.c

@@ -67,7 +67,7 @@ static GstStaticPadTemplate gst_msdkvpp_src_factory =
     GST_PAD_ALWAYS,
     GST_STATIC_CAPS (GST_VIDEO_CAPS_MAKE_WITH_FEATURES
         (GST_CAPS_FEATURE_MEMORY_DMABUF,
-            "{ BGRA, YUY2, NV12, P010_10LE}") ";"
+            "{ BGRA, YUY2, NV12, BGRx, P010_10LE}") ";"
         GST_VIDEO_CAPS_MAKE ("{ BGRA, NV12, YUY2, BGRx, P010_10LE }") ", "
         "interlace-mode = (string){ progressive, interleaved, mixed }" ";"));