x86: add x2apic config

Impact: cleanup

so could deselect x2apic
and INTR_REMAP will select x2apic

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>