drm/nvd0/disp: hopefully fix selection of 6/8bpc mode on DP outputs

I have a very limited number of traces available for DP on NVD9+, but,
these values produce the same as the binary driver on a confirmed 18-bit
eDP panel and a confirmed 24-bit eDP panel (Retina MBP).

It's interesting that the bitfield values also match the MODE_CTRL values
that control the same thing on nv50:nvd9.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvd0_display.c

@@ -1510,10 +1510,10 @@ nvd0_sor_mode_set(struct drm_encoder *encoder, struct drm_display_mode *umode,
 	case OUTPUT_DP:
 		if (nv_connector->base.display_info.bpc == 6) {
 			nv_encoder->dp.datarate = mode->clock * 18 / 8;
-			syncs |= 0x00000140;
+			syncs |= 0x00000002 << 6;
 		} else {
 			nv_encoder->dp.datarate = mode->clock * 24 / 8;
-			syncs |= 0x00000180;
+			syncs |= 0x00000005 << 6;
 		}
 
 		if (nv_encoder->dcb->sorconf.link & 1)