ARM: clocksource: Add asm9260_timer driver

In some cases asm9260 looks similar to iMX2x. One of exceptions is
timer controller. So this patch introduces new driver for this special case.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>