We've had the legacy platform code take care of suspend for us but
this no longer is the case when probed without legacy mode with
ti-sysc. We need to configure PM ops like standard Linux device
drivers do.

As we still have some SoCs booting also the legacy mode, we need to
add omap_gpio_suspend() and omap_gpio_resume(), and check for the
is_suspended flag to avoid legacy _od_suspend_noirq() calling them
on an already suspended GPIO instance.

Once we have no SoCs booting in legacy mode, we can just switch to
using the standard PM ops with pm_runtime_force_suspend() and
pm_runtime_force_resume().
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>