Then you need mesa with wayland support, i.e. "--with-egl-platforms=wayland,[drm,x11,…]", this uses wayland at compile time.
If I understand it correctly this should be enough to run "wayland". Of course you probably want a compositor like weston for that.
But... What about xwayland? How will this work with radeonsi? The xwayland website tells you to checkout a branch named xwayland-1.12 so it probably isn't a problem yet anyway, but with 1.13 a proper xf86-video-ati with xwayland support would need glamor too, right? I haven't heard anything about the performance of xf86-video-wlshm. Can it use the the 3d acceleration wayland "has"?