[POWERPC] ps3: Fix section mismatch in ps3/setup.c

WARNING: vmlinux.o(.text+0x605d4): Section mismatch: reference to
.init.text:.__alloc_bootmem (between '.prealloc' and '.ps3_power_save')

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>