ASoC: pcm512x: Remove hardcoding of pll-lock to GPIO4

Currently GPIO4 is hardcoded to output the pll-lock signal.
Unfortunately this is after the pll-out GPIO is configured which
is selectable in the device tree. Therefore it is not possible to
use GPIO4 for pll-out. Therefore this patch removes the
configuration of GPIO4.

Signed-off-by: Howard Mitchell <hm@hmbedded.co.uk>
Signed-off-by: Mark Brown <broonie@kernel.org>