drm/nouveau/kms: Start using drm_dp_read_dpcd_caps()

Now that we've extracted i915's code for reading both the normal DPCD
caps and extended DPCD caps into a shared helper, let's start using this
in nouveau to enable us to start checking extended DPCD caps for free.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200826182456.322681-21-lyude@redhat.com

drivers/gpu/drm/nouveau/nouveau_dp.c

@@ -54,15 +54,13 @@ nouveau_dp_probe_dpcd(struct nouveau_connector *nv_connector,
 	int ret;
 	u8 *dpcd = outp->dp.dpcd;
 
-	ret = drm_dp_dpcd_read(aux, DP_DPCD_REV, dpcd, DP_RECEIVER_CAP_SIZE);
-	if (ret == DP_RECEIVER_CAP_SIZE && dpcd[DP_DPCD_REV]) {
-		ret = drm_dp_read_desc(aux, &outp->dp.desc,
-				       drm_dp_is_branch(dpcd));
-		if (ret < 0)
-			goto out;
-	} else {
+	ret = drm_dp_read_dpcd_caps(aux, dpcd);
+	if (ret < 0)
+		goto out;
+
+	ret = drm_dp_read_desc(aux, &outp->dp.desc, drm_dp_is_branch(dpcd));
+	if (ret < 0)
 		goto out;
-	}
 
 	if (nouveau_mst) {
 		mstm = outp->dp.mstm;