drm/i915/display: convert intel_mode_valid_max_plane_size() to intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert the intel_mode_valid_max_plane_size() helper to struct
intel_display, allowing further conversions elsewhere.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/6e7810c793ecc8ff6a31569830bf162156245668.1739378095.git.jani.nikula@intel.com