gpio: tegra: Add support for gpio debounce

NVIDIA's Tegra210 support the HW debounce in the GPIO controller
for all its GPIO pins.

Add support for setting debounce timing by implementing the
set_debounce callback of gpiochip.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>