backend/wayland_egl: Add a fallback eglConfig

backend/wayland_egl: Add a fallback eglConfig

On agl-kvm-guest and agl-rdp, flutter-auto with its eglConfig will have
a black image as opposed to regular one. This is a work-around by
using a fallback eglConfig until flutter-auto gains some sort of
heuristic choosing between the eglConfig available and pick one that
can work.

Bug-AGL: SPEC-5260
Change-Id: I1f9f95d2bba1d218b9b1fb12ff11df3209dc2e03
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/30477
ci-image-build: Jenkins Job builder account
Tested-by: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>