libs: display: drm: allow user specify a drm device via an env variable
Currently the default drm device is always used on a system with multiple drm devices. This patch allows user to specify the required drm device via GST_VAAPI_DRM_DEVICE env variable
Example: GST_VAAPI_DRM_DEVICE=/dev/dri/renderD129 gst-launch-1.0 videotestsrc ! vaapih264enc ! fakesink
Edited by Haihao Xiang