mac_newworld: add via machine option to control mac99 VIA/ADB configuration

mac_newworld: add via machine option to control mac99 VIA/ADB configuration

This option allows the VIA configuration to be controlled between 3
different possible setups: cuda, pmu-adb and pmu with USB rather than ADB
keyboard/mouse.

For the moment we don't do anything with the configuration except to pass
it to the macio device (the via-cuda parent) and also to the firmware via
the fw_cfg interface so that it can present the correct device tree.

The default is cuda which is the current default and so will have no
change in behaviour.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>