arm64: dts: rockchip: assign a fixed index to mmc devices on rk3308 boards

Recently introduced async probe on mmc devices can shuffle block IDs.
Pin them to fixed values to ease booting in environments where UUIDs are
not practical. Use newly introduced aliases for mmcblk devices from [1].
The sort order is based on reg address.

[1] https://patchwork.kernel.org/patch/11747669/

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20210118155242.7172-4-jbx6244@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3308.dtsi

@@ -24,6 +24,9 @@
 		i2c1 = &i2c1;
 		i2c2 = &i2c2;
 		i2c3 = &i2c3;
+		mmc0 = &sdmmc;
+		mmc1 = &emmc;
+		mmc2 = &sdio;
 		serial0 = &uart0;
 		serial1 = &uart1;
 		serial2 = &uart2;