drm/tegra: Switch to using devm_fwnode_gpiod_get()

devm_gpiod_get_from_of_node() is going away and GPIO consumers should
use generic device/firmware node APIs to fetch GPIOs assigned to them.
Switch the driver to use devm_fwnode_gpiod_get() instead.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>