PLLs are the source clocks for the DDIs so in order to determine the
ddi clock we need to check the PLL configuration.

For MG PHy Ports (C - F), depending on whether it is a TBT PLL or MG
PLL the link lock can be obtained from the the PLL divisors based on
the specification.

v2 (from Paulo):
 * Make the algorithm look more like what's in the spec, also document
   where we differ form the spec and why.
 * Make the code a little more consistent with our coding style.
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180817215209.29133-2-paulo.r.zanoni@intel.com