x86, sfi: Use register_lapic_address()

register_lapic_address() and mp_sfi_register_lapic_address() are
almost identical. Use the common function.

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: <4CFDF693.6000908@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>