[MIPS] IP27: Fix modpost warning.

  MODPOST vmlinux.o
WARNING: vmlinux.o(.text+0x3180): Section mismatch: reference to .init.text:per_cpu_init (between 'prom_init_secondary' and 'alloc_cpupda')

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>