gpio: tegra: add gpio wakeup source handling

This patch add the gpio wakeup source handling for the Tegra platform. It
was be done by enabling the irq for the gpio in the gpio controller and
enabling the bank irq of the gpio in the Tegra legacy irq controller when
the system going to suspend.

Based on the work by:
Varun Wadekar <vwadekar@nvidia.com>

Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Joseph Lo <josephl@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>