x86: make sparse mem work in non-NUMA mode

With sparse memory, holes should not be marked present for memmap.
This patch makes sure sparsemem really works on SMP mode (!NUMA).

[ Impact: use less memory to map fragmented RAM, avoid boot-OOM/crash ]

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Sheng Yang <sheng.yang@intel.com>
LKML-Reference: <1242117600.22431.0.camel@sli10-desk.sh.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>