ASoC: tlv320aic31xx: Rename property for reset GPIO

ASoC: tlv320aic31xx: Rename property for reset GPIO

The property used to specify a GPIO intended for reset is "reset-gpios",
but this binding uses "gpio-reset".  It is not compatible with newer
methods used to fetch GPIO pins and to prevent the spread of this error
to other bindings let's rename to be more standard.

We also standardize the pin as active-low, different device trees have
marked the GPIO different ways, luckily the driver currently uses the
low-level GPIO set function which does not respect the active-low flag,
but future changes may change this. This is an active-low reset, mark
it as such.

Lastly, add an example of use for this property.

[Rewrote the title & first paragraph of the commit message for clarity
-- broonie]

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>