ui/dbus: fix compilation when GBM && !OPENGL

ui/dbus: fix compilation when GBM && !OPENGL

commit 4814d3cbf ("ui/dbus: restrict opengl to gbm-enabled config")
assumes that whenever GBM is available, OpenGL is. This is not always
the case, let's further restrict opengl-related paths and fix some
compilation issues.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230515132348.1024663-1-marcandre.lureau@redhat.com>
(cherry picked from commit 0b31e48d62c8f3a282d1bffbcc0e90200df9f9f0)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>