drm/i915/scaler: Extract skl_scaler_max_src_size()

The SKL_MAX_SRC_* defines just make things hard to read.
Get rid of them and introduce an easy to read function
in their place.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241219130827.22830-3-ville.syrjala@linux.intel.com


Reviewed-by: Luca Coelho <luciano.coelho@intel.com>