wpe: Add software rendering support
Starting from WPEBackend-FDO 1.6.x, headless support is available. This features
allows wpesrc to be used on machines without GPU, and/or for testing purpose. To
enable it, set the LIBGL_ALWAYS_SOFTWARE=true
environment variable and make
sure video/x-raw, format=BGRA
caps are negotiated by the wpesrc element.
Edited by Tim-Philipp Müller