pinctrl: tegra: Add support to display pin function

The current function for a given pin is not displayed via the debugfs.
Add support to display the current function that is set for each pin.

Signed-off-by: Prathamesh Shete <pshete@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20230714113547.15384-1-pshete@nvidia.com


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