powerpc: Initialize secondary CPU setup for 32-bit SMP

32-bit SMP powermacs weren't booting with ARCH=powerpc because the
boot cpu wasn't saving away the state of various control registers,
but the secondary CPUs were loading them from the uninitialized
state.  This adds the necessary save-state call.

Signed-off-by: Paul Mackerras <paulus@samba.org>