The wayland backend requires libxkbcommon, so when wayland is available
select it to avoid build failure and obscure dependencies. Fixes:
http://autobuild.buildroot.net/results/ed2/ed2660361c9720e48dd5959f2711fd7f14031b0d/
Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>