drm/i915: Extract glk_need_scaler_clock_gating_wa()

Simplify our life by extracting the "do we need the glk scaler
clock gating w/a?" check into a small helper.

Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240402135148.23011-5-ville.syrjala@linux.intel.com