Input: imx_keypad - remove ifdef round PM methods

We can annotate the suspend/resume functions with '__maybe_unused' and get
rid of the ifdef, which makes the code smaller and simpler.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>