Input: adp5588-keys - drop CONFIG_PM guards

To improve compile-time coverage let's drop #ifdef CONFIG_PM guards
and use SIMPLE_DEV_PM_OPS and __maybe_unused attributes and rely on
the linker to drop unused code.

Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://lore.kernel.org/r/20220528045631.289821-1-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>