[PATCH] powerpc: iseries: Remove pointless iSeries_(restart|power_off|halt)

These routines just call through to the mf routines, so point ppc_md straight
at the mf routines. We need to pass the cmd through to mf_reboot to make it
work, but that seems reasonable.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>