arm64: dts: specify 1.8V EMMC capabilities for bcm958742k

Specify 1.8V EMMC capabilities for bcm958742k board to indicate support
for UHS mode.

Fixes: d4b4aba6 ("arm64: dts: Initial DTS files for Broadcom Stingray SOC")
Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm64/boot/dts/broadcom/stingray/bcm958742k.dts

@@ -43,6 +43,10 @@ &gphy0 {
 	enet-phy-lane-swap;
 };
 
+&sdio0 {
+	mmc-ddr-1_8v;
+};
+
 &uart2 {
 	status = "okay";
 };