ASoC: core: Add snd_soc_of_parse_pin_switches() from simple-card-utils

The ASoC core already has several helpers to parse card properties
from the device tree. Move the parsing code for "pin-switches" from
simple-card-utils to a shared snd_soc_of_parse_pin_switches() function
so other drivers can also use it to set up pin switches configured in
the device tree.

Cc: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20211214142049.20422-2-stephan@gerhold.net
Signed-off-by: Mark Brown <broonie@kernel.org>