x86: reduce clock calibration time during slave cpu startup

x86: reduce clock calibration time during slave cpu startup

Reduce the startup time for slave cpus.

Adds hooks for an arch-specific function for clock calibration.  These
hooks are used on x86.  If a newly started cpu has the same phys_proc_id
as a core already active, uses the TSC for the delay loop and has a
CONSTANT_TSC, use the already-calculated value of loops_per_jiffy.

This patch reduces the time required to start slave cpus on a 4096 cpu
system from: 465 sec OLD 62 sec NEW

This reduces boot time on a 4096p system by almost 7 minutes.  Nice...

[akpm@linux-foundation.org: fix CONFIG_SMP=n build]
Signed-off-by: Jack Steiner <steiner@sgi.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>