mfd: tc6393xb: Remove #ifdef guards for PM related functions

Use the new pm_sleep_ptr() macro to handle the .suspend/.resume
callbacks.

This macro 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>