ASoC: pcm512x: Allow independently overclocking PLL, DAC and DSP

When using non-standard rates, a relatively small amount of overclocking
can make a big difference to a number of cases.

- Not all rates are possible to achieve with the PLL, due to divider
  restrictions.

- The higher oversampling rates that can be used by the DAC, the
  simpler the analog output filters get (mirror frequencies move up,
  away from the desired spectrum).

- The more work the DSP can perform per sample, the better.

For standard rates, there is little to gain as everything is
designed just right, and the needed overclocking to make a
real difference would be significant.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Mark Brown <broonie@kernel.org>