gbm: Enhance logging and add environment variable for selecting DRM connector
Submitted by Carlos Rafael Giani
Currently, the first connected DRM connector is selected. This may not always be the right one. For this reason, add a GST_GL_GBM_DRM_CONNECTOR environment variable that allows for selecting a connector by name.
Also improve GBM logging by always logging all DRM connectors, modes, encoders, even if some have already been selected.