[ARM] S3C64XX: Update TCFG for new timer divider settings.

The S3C64XX series has a new TCFG divider setting to allow the clock
directly through, which means that we need to update the pwm-clock
code to cope with this.

Add <mach/pwm-clock.h> containing the specific code to deal with the
TCFG divider settings and provide any other per-arch data that the
pwm-clock driver needs to function.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>