[POWERPC] PS3: Repository probe cleanups

Repository updates:
  - Extract ps3_repository_find_bus() from ps3_repository_find_device(), as the
    storage driver needs it.
  - Make ps3_repository_find_device() return -ENODEV if a device is not found,
    just like if a bus is not found.
  - Add ps3_repository_read_vuart_sysmgr_port() and
    ps3_repository_read_vuart_av_port() to get vuart port info.
  - Add device enumeration routines ps3_repository_find_device() and
    ps3_repository_find_devices().
  - Cleanup debug routines.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>