rockchip: rk3399: enable spl-fifo-mode for sdmmc

adapting commit fa2047c4 ("rockchip: rk3328: enable spl-fifo-mode
for emmc and sdmmc") for rk3399.
Since mmc to sram can't do dma, add patch to prevent aborts transferring
TF-A parts.
Signed-off-by: NDeepak Das <deepakdas.linux@gmail.com>

arch/arm/dts/rk3399-u-boot.dtsi

@@ -91,6 +91,9 @@
 
 &sdmmc {
 	u-boot,dm-pre-reloc;
+
+	/* mmc to sram can't do dma, prevent aborts transferring TF-A parts */
+	u-boot,spl-fifo-mode;
 };
 
 &spi1 {