[POWERPC] iSeries: Fix section mismatch warnings

WARNING: vmlinux.o(.text+0x8124): Section mismatch: reference to .init.text:.iSeries_early_setup (between '.__start_initialization_iSeries' and '.__mmu_off')
WARNING: vmlinux.o(.text+0x8128): Section mismatch: reference to .init.text:.early_setup (between '.__start_initialization_iSeries' and '.__mmu_off')

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