x86, mm: relocate initrd under all mem for 64bit

instead of under 4g.

For 64bit, we can use any mapped mem instead of low mem.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1353123563-3103-17-git-send-email-yinghai@kernel.org


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>