As both pxa and sa1100 provide a clock to the timer, the rate can be
inferred from the clock rather than hard encoded in a functional call.

This patch changes the pxa timer to have a mandatory clock which is used
as the timer rate.
Signed-off-by: NRobert Jarzmik <robert.jarzmik@free.fr>
Acked-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: NRussell King <rmk+kernel@armlinux.org.uk>