Add x2apic_supported() to clean up CONFIG_X86_X2APIC checks.

Fix CONFIG_INTR_REMAP checks.

[ Impact: cleanup ]
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: dwmw2@infradead.org
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Weidong Han <weidong.han@intel.com>
LKML-Reference: <20090420200450.128993000@linux-os.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>