x86: make amd quad core 8 socket system not be clustered_box, #2

quad core 8 socket system will have apic id lifting.the apic id range could
be [4, 0x23]. and apic_is_clustered_box will think that need to three clusters
and that is large than 2. So it is treated as clustered_box.

and will get

Marking TSC unstable due to TSCs unsynchronized

even the CPUs have X86_FEATURE_CONSTANT_TSC set.

this patch will check if the cpu is from AMD.

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>