clocksource: owl: Add S900 support

The Actions Semi S900 SoC provides four 32-bit timers, TIMER0/1/2/3,
but no 2Hz timers.

An S900 datasheet can be found in 96Boards documentation:
https://github.com/96boards/documentation/blob/master/ConsumerEdition/Bubblegum-96/HardwareDocs/SoC_bubblegum96.pdf



Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>