drm/i915: Refactor skl+ plane register offset calculations

Currently every skl+ plane register defines some intermediate
macros to calculate the final register offset. Pull all of that
into common macros, simplifying the final register offset stuff
into just five defines:
- raw register offsets for the planes 1 and 2 on pipes A and B
- the final parametrized macro

v2: Rebase
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240513170040.15393-1-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>