Don't rely on CPU cycles to measure time.

We have a proper clocksource in the kernel, use this instead.

This commit also fixes jackd on ARM boards with newer Linux kernels
where /proc/cpuinfo has changed.

Cross-ported from jackd1.
Make -c c an alias for -c s

The cycle counting clock is no longer supported. For backwards
compatibility with scripts, allow the user to request the cycle clock on
the command line, but use the system clock instead.

Cross-ported from jackd1.
Drop (c)ycle) from the list of allowed clock sources.
Drop JACK_TIMER_CYCLE_COUNTER altogether
Update manpage to reflect dropped -c c option