doc: Document which options are disabled by mClock.

doc: Document which options are disabled by mClock.

Not only in the mClock docs, but also in the reference
of the options that are disabled.

Otherwise users are bound to miss it, and surprised
why their options are ignored or reset.

Signed-off-by: Niklas Hambüchen <mail@nh2.me>
(cherry picked from commit 790afd277730f24801a3b59c08d2dce0f2a9659f)