ARM: use device tree to get smp_twd clock

Move clk setup to twd_local_timer_common_register and rely on
twd_timer_rate being 0 to force calibration if there is no clock.
Remove common_setup_called as it is no longer needed.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>