ARM: pxa: Add non device-tree timer link to clocksource

As clocksource pxa_timer was moved to clocksource framework, the
pxa_timer initialization needs to be a bit amended, to pass the
necessary informations to clocksource, ie :
 - the timer interrupt (mach specific)
 - the timer registers base (ditto)
 - the timer clockrate

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>