clocksource/drivers/arm_arch_timer: Advertise 56bit timer to the core code

Proudly tell the code code that we have a timer able to handle
56 bits deltas.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211017124225.3018098-9-maz@kernel.org


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>