Update openbios-ppc to revision 418

- fix milliseconds PROM call
- fix PCI I/O ports assignation
- misc fixes

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6363 c046a42c-6fe2-441c-8c8c-71466251a162