CLOCKSOURCE: mips-gic: Update clockevent frequency on clock rate changes

This commit introduces the clockevent frequency update, using
a clock notifier. It will be used to support CPUFreq on platforms
using MIPS GIC based clockevents.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: James Hartley <James.Hartley@imgtec.com>
Cc: Govindraj Raja <Govindraj.Raja@imgtec.com>
Cc: Damien Horsley <Damien.Horsley@imgtec.com>
Cc: James Hogan <James.Hogan@imgtec.com>
Cc: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Patchwork: https://patchwork.linux-mips.org/patch/10782/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>