ARM: dts: socfpga: add cap-sd-highspeed for SD/MMC node

Enable SD highspeed support for the SoCFPGA Arria10 devkit.
Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>

arch/arm/boot/dts/socfpga_arria10_socdk_sdmmc.dts

@@ -21,6 +21,7 @@
 &mmc {
 	status = "okay";
 	num-slots = <1>;
+	cap-sd-highspeed;
 	broken-cd;
 	bus-width = <4>;
 };