Add r-ccu support for the Allwinner a83t

The r-ccu on the a83t differs from the others only by what it names the
ar100 parents. Export the _CCU macros (now converted to an enu) so that
ccu_sun8i_r can differentiate between a83t r-ccu and the others, then add
the compat string for the a83t r-ccu.

Reviewed by: manu
Approved by: emaste (mentor, implicit)
Differential Revision: https://reviews.freebsd.org/D13206