[POWERPC] Move MPIC smp routines into mpic.c

Move a couple of MPIC smp routines into mpic.c, they're inside an SMP
block in mpic.c - so they're still only built for SMP.

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