[POWERPC] Fix celleb pci section warnings

Fix following warnings:
WARNING: vmlinux.o(.text+0x44ad0): Section mismatch: reference to .init.text:.__alloc_bootmem (between '.celleb_setup_phb' and '.celleb_fake_pci_write_config')
WARNING: vmlinux.o(.text+0x44dd8): Section mismatch: reference to .init.text:.free_bootmem (between '.celleb_setup_phb' and '.celleb_fake_pci_write_config')

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Paul Mackerras <paulus@samba.org>