drm/komeda: Add runtime_pm support

- Add pm_runtime_get/put to crtc_enable/disable along with the real
  display usage
- Add runtime_get/put to register_show, since register_show() will
  access register, need to wakeup HW.
- For the case that PM is not enabled or configured, manually wakeup HW

Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Reviewed-by: Mihail Atanassov <mihail.atanassov@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191212074756.14678-1-james.qian.wang@arm.com