[WATCHDOG] CPUFREQ: S3C24XX Watchdog frequency scaling support.

Add support for CPU frequency scaling to the S3C24XX Watchdog
driver.

Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>