drm/i915/icl: Refactor icl pll functions

This patch adds helper function for identifying
whether the given PLL is combo PHY PLL or not.
This helper function is used inside various ICL
functions to make them scalable.

Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: Madhav Chauhan <madhav.chauhan@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181003072203.12848-6-mahesh1.kumar@intel.com