Enforcing a primary+leaf configuration does not walk for all the cases.
Some clocks (msm8996 CPU) have more muxes to be powered on. Other (MCCC)
do not require GCC at all. Make clock measurement more versatile by
reworking GCC + optional leaf into a chain of muxes.
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
