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

Use the new EXPORT_GPL_SIMPLE_DEV_PM_OPS() and pm_sleep_ptr() macros
to handle the .suspend/.resume callbacks.

These macros allow the suspend and resume functions to be automatically
dropped by the compiler when CONFIG_SUSPEND 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.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Lee Jones <lee@kernel.org>