introducing an APIC handling probing abstraction:

 static struct genapic *apic_probe[] __initdata = {
	&apic_x2apic_uv_x,
	&apic_x2apic_phys,
	&apic_x2apic_cluster,
	&apic_physflat,
	NULL,
 };

This way we can remove UV, x2apic specific code from genapic_64.c and
move them to their specific genapic files.

[ v2: fix compiling when CONFIG_ACPI is not set ]
Signed-off-by: NYinghai Lu <yhlu.kernel@gmail.com>
Cc: Jack Steiner <steiner@sgi.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

generalize the x2apic code some more.

let read_apic_id become a macro (later on a function/inline)
GET_APIC_ID(apic_read(APIC_ID))

  +#define read_apic_id()  (GET_APIC_ID(apic_read(APIC_ID)))

instead of this weird construct:

  -#define read_apic_id  (genapic->read_apic_id)
Signed-off-by: NYinghai Lu <yhlu.kernel@gmail.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

x2apic Physical mode  support. By default we will use x2apic cluster mode.
x2apic physical mode can be selected using "x2apic_phys" boot parameter.
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Cc: akpm@linux-foundation.org
Cc: arjan@linux.intel.com
Cc: andi@firstfloor.org
Cc: ebiederm@xmission.com
Cc: jbarnes@virtuousgeek.org
Cc: steiner@sgi.com
Signed-off-by: NIngo Molnar <mingo@elte.hu>

x2apic cluster mode support.
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Cc: akpm@linux-foundation.org
Cc: arjan@linux.intel.com
Cc: andi@firstfloor.org
Cc: ebiederm@xmission.com
Cc: jbarnes@virtuousgeek.org
Cc: steiner@sgi.com
Signed-off-by: NIngo Molnar <mingo@elte.hu>