rockchip: Pinebook Pro: Enable edp

- uboot rockchip edp code is looking for a rockchip,panel property
  for the edp dts node, so add it.
Signed-off-by: NArnaud Patard <arnaud.patard@rtp-net.org>
Tested-by: NPeter Robinson <pbrobinson@gmail.com>

arch/arm/dts/rk3399-pinebook-pro-u-boot.dtsi

@@ -16,6 +16,10 @@
 	};
 };
 
+&edp {
+	rockchip,panel = <&edp_panel>;
+};
+
 &i2c0 {
 	u-boot,dm-pre-reloc;
 };