drm/i915: Clean up glk_pipe_scaler_clock_gating_wa()

glk_pipe_scaler_clock_gating_wa() is messy. Clean it up via
intel_de_rmw(), and also just pass in the whole crtc so the
caller doesn't have to dance around so much.

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/20240402135148.23011-4-ville.syrjala@linux.intel.com