This break-out from Colin Cross' cpufreq-aware TWD patch
will handle the case when our localtimer's clock changes with
the cpu clock. A cpufreq transtion notifier will be registered
only if the platform has supplied a specified clock to the TWD.

After a cpufreq transition, update the clockevent's frequency
by fetching the new clock rate from the clock framework and
reprogram the next clock event.

The necessary changes in the clockevents framework was done by
Thomas Gleixner in kernel v3.0.

ChangeLog v1->v2:
- Replace IS_ERR_OR_NULL() with IS_ERR() in twd_clk check.
- Update code to use the already existing per-cpu array of TWD
  clockevents instead of adding cruft.

[Broke out, ifdef:ed CPUfreq stuff for non-cpufreq configs]
[Rebased to newer TWD base with per-CPU clock array]
Signed-off-by: Colin Cross <ccross@android.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>