gcr: Require x11 DISTRO_FEATURE

This enables a world build without x11. GTK3DISTROFEATURES is not
enough because gtk+-x11.pc is still required.

Fixes [YOCTO #8611].

Signed-off-by: Jussi Kukkonen <jussi.kukkonen@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>