clocksource/drivers/arm_arch_timer: Map frame with of_io_request_and_map()

Let's use the of_io_request_and_map() API so that the frame
region is protected and shows up in /proc/iomem.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>