aw_ccung: changes to accommodate upcoming a83t support

Add a means to specify mask/value for the prediv condition instead of
shift/width/value for clocks that have a more complex mux scenario.

Specifically, ahb1 on the a83t has the prediv applied if mux is either b10
or b11.

Reviewed by: manu
Approved by: emaste (mentor)
Differential Revision: https://reviews.freebsd.org/D12851