dt-bindings: gpio: nxp,pcf8575: add gpio-line-names

The devices described in this binding represent 8-bit and 16-bit i2c i/o
expanders. Allow the user to specify names for up to 16 gpio lines.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230210025132.36605-1-twoerner@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>