pinctrl: tegra: debugfs enhancements

* Only provide debugfs-relates ops when CONFIG_DEBUG_FS is enabled.
* Implement pin_config_group_dbg_show op.
* Implement pin_config_config_dbg_show op.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>