Draft: [amd64] Enable Intel Low Power Subsystem driver as built-in

Task https://phabricator.collabora.com/T36286

Enable driver for Intel Low Power Subsystem (LPSS) devices as built-in, so HS-UART (i.e. debug console) is brought up on boot, without needing to load the module.

This is useful to boot initrd's and systems that might not include the driver module, but we still get access to the debug console.