[MIPS] Alchemy: Fix modpost warnings.

  MODPOST vmlinux
WARNING: arch/mips/au1000/common/built-in.o(.text+0x1750): Section mismatch: reference to .init.data: (between 'au1xxx_platform_init' and '__fixup_bigphys_addr')
WARNING: arch/mips/au1000/common/built-in.o(.text+0x1754): Section mismatch: reference to .init.data: (between 'au1xxx_platform_init' and '__fixup_bigphys_addr')

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