pinctrl: meson: meson8: add support for the I2S and SPDIF pins

This adds support for the I2S and SPDIF input and output pins, similar
to what we have on GXBB and GXL.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>