ASoC: pcm512x: Support mastering BCLK/LRCLK without using the PLL

Use register field names from the seemingly compatible PCM5242 datasheet,
as the PCM512x and PCM514x datasheets are severly lacking.

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