clocksource: cris: Convert to clocksource_register_khz

This converts the cris architecture to use clocksource_register_khz

This is untested, so any help from maintainers would be appreciated.

CC: Mikael Starvik <starvik@axis.com>
CC: Jesper Nilsson <jesper.nilsson@axis.com>
CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>