arm64: dts: hikey: Enable HS200 mode on eMMC

According to the hi6220 datasheet, the MMC controller is JEDEC eMMC 4.5
compliant, in addition to supporting a clock of up to 150MHz. The Hikey
schematic also indicates the device utilizes 1.8v signaling. Define these
parameters in the device tree to enable HS200 mode.
Signed-off-by: Ryan Grachek <ryan@edited.us>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

arch/arm64/boot/dts/hisilicon/hi6220-hikey.dts

@@ -299,7 +299,9 @@ gpio15: gpio@f702b000 {
 		/* GPIO blocks 16 thru 19 do not appear to be routed to pins */
 
 		dwmmc_0: dwmmc0@f723d000 {
+			max-frequency = <150000000>;
 			cap-mmc-highspeed;
+			mmc-hs200-1_8v;
 			non-removable;
 			bus-width = <0x8>;
 			vmmc-supply = <&ldo19>;