[POWERPC] ps3: Add vuart support

Adds support for the PS3 virtual UART (vuart).  The vuart provides a
bi-directional byte stream data link between logical partitions.

This is needed for the ps3 graphics driver and the ps3 power
control support to be able to communicate with the lv1 policy
module.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>