The CDCLK bypass frequency can vary on upcoming platforms, so prepare
for that now by tracking its value in the CDCLK state.

Currently on BDW+ the bypass frequency is always the reference clock and
I didn't bother with earlier platforms since it's not all that clear
what's the bypass clock on those.

I also didn't bother adding support for changing this frequency, since
atm I don't see any need for it.
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180117172508.15993-1-imre.deak@intel.com