rockchip: firefly-rk3399: dts: enable sdmmc device

Enable sdmmc device and add the spl boot device sequence.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

arch/arm/dts/rk3399-firefly.dts

@@ -16,6 +16,7 @@
 
 	chosen {
 		stdout-path = &uart2;
+		u-boot,spl-boot-order = &sdhci, &sdmmc;
 	};
 
 	backlight: backlight {
@@ -590,6 +591,12 @@
 	status = "okay";
 };
 
+&sdmmc {
+	u-boot,dm-pre-reloc;
+	bus-width = <4>;
+	status = "okay";
+};
+
 &sdhci {
 	bus-width = <8>;
 	keep-power-in-suspend;