Yifan Zhu accepted merge request !381: :cherries: skip ddcutil initialization when POWERDEVIL_NO_DDCUTIL is set at Plasma / PowerDevil

When POWERDEVIL_NO_DDCUTIL is set, the platform initialization should beskipped entirely. This restores the old behavior beforea6b9cf5f.

CCBUG: 488373

(cherry picked from commit 40625d03)

Co-authored-by: Yifan Zhu

I plan to merge after the 6.1 release; targetting 6.1.1.