clocksource/drivers/sprd: Register one always-on timer to compensate suspend time

Since the clocksource framework has introduced one suspend clocksource to
compensate the suspend time, this patch registers one always-on timer as
the suspend clocksource.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>