ARM: sirf: use clocksource_of infrastructure

This moves the two sirf clocksource drivers to drivers/clocksource
and integrates them into the framework for locating the clock sources
automatically.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Barry Song <Baohua.Song@csr.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>