Input: omap4-keypad - wire up runtime PM handling

Enable Runtime PM functionality in OMAP4 driver based on the following
assumptions:

- keyboard controller in wakeup domain so it is always on and power
  impact is minimal;
- in OMAP4 the device control is at module/device level and ick/fclk
  level control is difficult so cutting of clocks will prevent
  interrupts.

Signed-off-by: Abraham Arce <x0066660@ti.com>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>