ASoC: nau8825: change crosstalk-bypass property to bool type

The property type of "nuvoton,crosstalk-bypass" changes to boolean.
The document is updated as well.

Signed-off-by: John Hsu <KCHSU0@nuvoton.com>
Signed-off-by: John Hsu <supercraig0719@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>