gpio: ml-ioh: Convert to dev_pm_ops

Convert the legacy callback .suspend() and .resume()
to the generic ones.

While at it, replace ifdeffery by __maybe_unused attribute.

Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>