services: xorg: Filter modules based on system

services: xorg: Filter modules based on system

Fixes <https://bugs.gnu.org/39402>.
Reported by shtwzrd <shtwzrd@protonmail.com>.

* gnu/services/xorg.scm (xorg-configuration):
  Apply a filter over %default-xorg-modules packages, excluding
  those for which the %current-system is not among the package's
  supported-systems.

This patch makes it possible to use xorg-configuration on systems
other than x86_64 and i686, as without it, xf86-video-intel would
be pulled in on the unsupported architecture and fail.

Signed-off-by: Jakub Kądziołka <kuba@kadziolka.net>