x86_64: Remove APIC_DIVISOR

APIC_DIVISOR is rather useless. It makes the calibration result more
accurate in the first place, but we discard this later when we write
the value to the APIC timer by dividing the calibration value by
APIC_DIVISOR.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>