The DDX'es sometimes need to disable certain extensions. Instead of complex
include cascades with ifdef'ed ddx-specific include from dix code, it's
more clean to add some clear and explicit knobs set by the DDX'es individual
meson.build.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1401>