drivers: gpio: stm32: fix init power state

Set suspended as initial power state, only when the
CONFIG_PM_DEVICE_RUNTIME config is enabled.

The initial state was incorrect, when CONFIG_PM_DEVICE=y and
CONFIG_PM_DEVICE_RUNTIME=n. In that case, the power state was SUSPENDED,
but the device was actually enabled.

Signed-off-by: Dawid Niedzwiecki <dawidn@google.com>