x86-common.yaml: Add kms platform plugin

All x86 adapations need kms platform plugin for the QML compositor.
Add maui-mic-plugins instructions
Add kde5 repository
Add ux-plasma repository
maui.yaml: Replace Hawaii with future KF5 & Plasma based shell

At the moment we just include sddm from ux-plasma repository.
It requires Xorg because at the moment Wayland is not supported by
Plasma shells.
services-x86-livecd.post: Enable sddm

Enable sddm for live CDs too.