gpio: omap: Fix warnings if PM is disabled

Fix warnings for omap_gpio_resume and omap_gpio_suspend
defined but not used when PM is disabled as noticed when
doing make randconfig builds.

Fixes: f02a0398 ("gpio: omap: Add missing PM ops for suspend")
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>