[POWERPC] Fix section mismatch in pasemi/iommu.c

These functions are only called by __init functions.

WARNING: vmlinux.o(.text+0x56aa0): Section mismatch: reference to .init.text:.lmb_alloc (between '.iob_init' and '.iommu_init_early_pasemi')

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>