drm/i915: Carve up struct intel_dpll_hw_state

drm/i915: Carve up struct intel_dpll_hw_state

struct intel_dpll_hw_state has a spot for all possible
PLL registers across all platforms (well, apart from
cx0/snps). This makes it rather confusing when trying to
figure out which members belong to which platform(s).

Split the struct up into five different platform specific
sub-structures. For now this will actually increase the size
a little bit as we have to duplicate a few members from
skl to icl, but that will be remedied soon when we turn
the thing into a union.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240412182703.19916-17-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>