Follow-up from "lenovo-dytc: Implement perfmode"

The following discussion from !15 (merged) should be addressed:

• @benzea started a discussion: (+4 comments)

  The problem here is that the user can press Fn+[LMH] at any point. And then the firmware will switch dytc_perfmode behind our back to the user selected value. And in that case we currently end up with a mismatch between firmware state and what the UI shows.