Use it to get mem size under the limit_pfn.
to replace local version in x86 reserved_initrd.

-v2: remove not needed cast that is pointed out by HPA.
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1359058816-7615-29-git-send-email-yinghai@kernel.orgSigned-off-by: NH. Peter Anvin <hpa@linux.intel.com>