drm/i915: Split cursor alignment to per-platform vfuncs

Split intel_cursor_alignment() into per-platform variants.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240612204712.31404-6-ville.syrjala@linux.intel.com