gpio: tegra: fix suspend/resume apis

Following are changes done to fix the suspend/resume
functionality of tegra gpio driver:
- Protect suspend/resume callbacks with CONFIG_PM_SLEEP
  because CONFIG_PM doesn't actually enable any of the PM callbacks, it
  only allows to enable CONFIG_PM_SLEEP and CONFIG_PM_RUNTIME.
  This means if CONFIG_PM is used to protect system sleep callbacks
  then it may end up unreferenced if only runtime PM is enabled.

- Fix the suspend/resume APIs declaration as per callback prototype.

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