drm/i915: Add PLL .compare_hw_state() vfunc

Chunk up the humongous dpll_hw_state comparison check into per-platform
variants, implemented in the dpll_mgr. This is step one in allowing
each platform (or perhaps even PLL) type to have a custom hw state
structure instead of having to smash it all into one.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240209183809.16887-5-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>