Plane .max_stride() is already a vfunc so having one made
up of two branches based on the display version is silly.
Split i9xx_plane_max_stride() into gen2 vs. gen3 variants
so  that we get rid of said check.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240506125718.26001-2-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>