ARM: dts: socfpga: enable MMC highspeed support

Add 'cap-mmc-highspeed' property to enable high-speed support for MMC cards.
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>

arch/arm/boot/dts/socfpga_arria10_socdk_sdmmc.dts

@@ -9,6 +9,7 @@
 &mmc {
 	status = "okay";
 	cap-sd-highspeed;
+	cap-mmc-highspeed;
 	broken-cd;
 	bus-width = <4>;
 };