x86, apic: Unify identical register_lapic_address() functions

They are the same, move the common function to apic.c to allow
further cleanups.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Len Brown <lenb@kernel.org>
LKML-Reference: <4CFDF675.4060305@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>