arm64: dts: renesas: r8a774b1-hihope-rzg2n: Enable HS400 mode

This patch enables HS400 mode on HiHope RZ/G2N board.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1569837778-55874-1-git-send-email-biju.das@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/arm64/boot/dts/renesas/r8a774b1-hihope-rzg2n.dts

@@ -24,3 +24,7 @@ memory@480000000 {
 		reg = <0x4 0x80000000 0x0 0x80000000>;
 	};
 };
+
+&sdhi3 {
+	mmc-hs400-1_8v;
+};