clk: bcm21664: use common clock framework

Define the set of CCUs and provided clocks sufficient to satisfy the
needs of all the existing clock references for BCM21664.  Replace
the "fake" fixed-rate clocks used previously with "real" ones.

Note that only the minimal set of these clocks and CCUs is defined
here.  More clock definitions will need to be added as required by
the addition of additional drivers.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>