x86: Use the generic page_is_ram()

The generic resource based page_is_ram() works better with memory
hotplug/hotremove. So switch the x86 e820map based code to it.

CC: Andi Kleen <andi@firstfloor.org>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
LKML-Reference: <20100122033004.470767217@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>