pinctrl: tegra: Display pin function in pinconf-groups

The function that a pin is muxed to can be read from the top-level
pinctrl-maps debugfs file. However, this only reflects the values that
were specified in device tree, so they will only show deviations from
the hardware default setting. Display the current pinmux setting in the
per-controller pinconf-groups debugfs file along with the rest of the
per-pin configuration settings.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20230929122101.466266-1-thierry.reding@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>