rockchip: dts: rk3328: add aliases for mmc controller

Add aliases for mmc controller to get a fixed order with
emmc at index 0 and sdmmc at index 1.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/dts/rk3328.dtsi

@@ -25,6 +25,9 @@
 		i2c1 = &i2c1;
 		i2c2 = &i2c2;
 		i2c3 = &i2c3;
+		mmc0 = &emmc;
+		mmc1 = &sdmmc;
+		mmc2 = &sdmmc_ext;
 	};
 
 	cpus {