MIPS/Malta: Probe gic-timer via devicetree

The Malta platform is the only platform remaining to probe the GIC
clocksource via gic_clocksource_init. This route hardcodes an expected
virq number based on MIPS_GIC_IRQ_BASE, which can be fragile to the
eventual virq layout. Instread, probe the driver using the preferred and
more modern devicetree method.

Before the driver is probed, set the "clock-frequency" property of the
devicetree node to the value detected by Malta platform code.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Link: http://lkml.kernel.org/r/1492604806-23420-1-git-send-email-matt.redfearn@imgtec.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>