Commit 712ec30cd9 added the logic to only
choose EGL configs that match the GBM_FORMAT_XRGB8888 pixel format.
However, there won't be any EGL config satisfying such criteria for
non-GBM backends, such as EGLDevice.
This change will let us choose the first EGL config for the EGLDevice
backend, while still forcing GBM_FORMAT_XRGB8888 configs for the GBM
one.
Related to: https://gitlab.gnome.org/GNOME/mutter/issues/2
(cherry picked from commit 1bf2eb95b5)
c647bd7807