x11: Use standalone xwayland package

The standalone package of xwayland is preffered over the package from xserver-xorg.

See https://git.yoctoproject.org/poky/commit/meta/recipes-graphics/ xwayland?h=kirkstone&id=07d33c8ec848c257c014fbef1241104847873d5f and https://fedoraproject.org/wiki/Changes/XwaylandStandalone