Re-enable wayland support
Previous commit accidentally disabled all of wayland support, instead of
just dropping mesa-libwayland-egl subpackage. This now re-enables
wayland support and reworks the conditionals so that we only drop drop
mesa-wayland-egl subpackage in F28+, where it is now part of wayland
source package.
https://bugzilla.redhat.com/show_bug.cgi?id=1564210