mfd: wm8994: Remove #ifdef guards for PM related functions

Use the new RUNTIME_PM_OPS() and pm_ptr() macros to handle the
.runtime_suspend/.runtime_resume callbacks.

These macros allow the suspend and resume functions to be automatically
dropped by the compiler when CONFIG_PM is disabled, without having
to use #ifdef guards.

This has the advantage of always compiling these functions in,
independently of any Kconfig option. Thanks to that, bugs and other
regressions are subsequently easier to catch.

Note that this driver should probably use the new
DEFINE_RUNTIME_DEV_PM_OPS() macro instead, which will provide
.suspend/.resume callbacks, pointing to pm_runtime_force_suspend() and
pm_runtime_force_resume() respectively; unless those callbacks really
aren't needed.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee@kernel.org>