xwayland: Fix build without glamor

Present support in Xwayland relies on glamor, make sure Xwayland can
be built without glamor by moving references to Present code inside
the conditional GLAMOR_HAS_GBM.

Reported-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Roman Gilg <subdiff@gmail.com>