drm/ingenic: Use the new PM macros

- Use DEFINE_SIMPLE_DEV_PM_OPS() instead of the SIMPLE_DEV_PM_OPS()
  macro. This makes it possible to remove the __maybe_unused flags on
  the callback functions.
- Since we only have callbacks for suspend/resume, we can conditionally
  compile the dev_pm_ops structure for when CONFIG_PM_SLEEP is enabled;
  so use the pm_sleep_ptr() macro instead of pm_ptr().

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220708205406.96473-7-paul@crapouillou.net