arm: dts: socfpga: Add mmc alias

Add alias for the SD/MMC controller, so it can be located by U-Boot OF support.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>

arch/arm/dts/socfpga.dtsi

@@ -23,6 +23,7 @@
 		spi0 = &qspi;
 		spi1 = &spi0;
 		spi2 = &spi1;
+		mmc = &mmc;
 	};
 
 	cpus {