egl/wayland: Add support for render-nodes

egl/wayland: Add support for render-nodes

It is possible the server advertises a render-node.
In that case no authentication is needed,
and Gem names are forbidden.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>
v2: do not check for __DRI_IMAGE_DRIVER, but instead
do not advertise __DRI_DRI2_LOADER when on a render-node.