rockchip: dts: rk3399: Add spl-boot-order for Rock PI 4

RK3399 use sdhci for eMMC and DW MMC for SD Card, and
spl will only try to boot from SDMMC if we don't specify
other boot device for spl-boot-order. So add sdhci and sdmmc
for spl-boot-order here.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

arch/arm/dts/rk3399-rock-pi-4-u-boot.dtsi

@@ -4,3 +4,8 @@
  */
 
 #include "rk3399-u-boot.dtsi"
+/ {
+	chosen {
+		u-boot,spl-boot-order = &sdhci, &sdmmc;
+	};
+};