x86/mm: Fix section mismatch derived from native_pagetable_reserve()

With CONFIG_DEBUG_SECTION_MISMATCH=y I see these warnings in next-20110415:

  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: vmlinux.o(.text+0x1ba48): Section mismatch in reference from the function native_pagetable_reserve() to the function .init.text:memblock_x86_reserve_range()
The function native_pagetable_reserve() references
the function __init memblock_x86_reserve_range().
This is often because native_pagetable_reserve lacks a __init
annotation or the annotation of memblock_x86_reserve_range is wrong.

This patch fixes the issue.
Thanks to pipacs from PaX project for help on IRC.

Acked-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>