clocksource: mips-gic: Move gic_frequency to clocksource driver

clocksource: mips-gic: Move gic_frequency to clocksource driver

There's no reason for gic_frequency to be global any more and it
certainly doesn't belong in the GIC irqchip driver, so move it to
the GIC clocksource driver.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Qais Yousef <qais.yousef@imgtec.com>
Cc: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8137/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>