drm/i915/mso: using joiner is not possible with eDP MSO

It's not possible to use the joiner at the same time with eDP MSO. When
a panel needs MSO, it's not optional, so MSO trumps joiner.

v3: Only change intel_dp_has_joiner(), leave debugfs alone (Ville)

Fixes: bc71194e8897 ("drm/i915/edp: enable eDP MSO during link training")
Cc: <[e-mail]> # v5.13+
Cc: Ville Syrjala <[e-mail]>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1668
Reviewed-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Jani Nikula <[e-mail]>
(cherry picked from commit 8b5a92ca24eb96bb71e2a55e352687487d87687f)
Signed-off-by: Jani Nikula <[e-mail]>

drivers/gpu/drm/i915/display/intel_dp.c

···
 	struct intel_encoder *encoder = &intel_dig_port->base;
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 
+	/* eDP MSO is not compatible with joiner */
+	if (intel_dp->mso_link_count)
+		return false;
+
 	return DISPLAY_VER(dev_priv) >= 12 ||
 		(DISPLAY_VER(dev_priv) == 11 &&
 		 encoder->port != PORT_A);