x86: use reserve_bootmem_generic() to reserve crashkernel memory on x86_64

This patch uses reserve_bootmem_generic() instead of reserve_bootmem()
to reserve the crashkernel memory on x86_64. That's necessary for NUMA
machines, see 00212fef

:

  [PATCH] Fix kdump Crash Kernel boot memory reservation for NUMA machines

  This patch will fix a boot memory reservation bug that trashes memory on
  the ES7000 when loading the kdump crash kernel.

  The code in arch/x86_64/kernel/setup.c to reserve boot memory for the crash
  kernel uses the non-numa aware "reserve_bootmem" function instead of the
  NUMA aware "reserve_bootmem_generic".  I checked to make sure that no other
  function was using "reserve_bootmem" and found none, except the ones that
  had NUMA ifdef'ed out.

  I have tested this patch only on an ES7000 with NUMA on and off (numa=off)
  in a single (non-NUMA) and multi-cell (NUMA) configurations.

Signed-off-by: Amul Shah <amul.shah@unisys.com>
  Looks-good-to: Vivek Goyal <vgoyal@in.ibm.com>
  Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

The switch-back to reserve_bootmem() was accidentally introduced in
5c3391f9

 when adding the BOOTMEM_EXCLUSIVE
parameter.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>