gpio: gpio-omap: add check for off wake capable gpios

We are currently assuming all GPIOs are non-wakeup capable GPIOs as we
not configuring the bank->non_wakeup_gpios like we used to earlier with
platform_data.

Let's add omap_gpio_is_off_wakeup_capable() to make the handling clearer
while considering that later patches may want to configure SoC specific
bank->non_wakeup_gpios for the GPIOs in wakeup domain.

Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Keerthy <j-keerthy@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Tero Kristo <t-kristo@ti.com>
Reported-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>