It disables PREBOOT enabled in:
https://github.com/u-boot/u-boot/commit/f81f9f0ebac596bae7f27db095f4f0272b606cc3

Booting with PREBOOT enabled leads to boot hangs at:
"Booting using the fdt blob at 0x1f00000"

Signed-off-by: Piotr Szczepanik <piter75@gmail.com>

diff --git a/configs/rockpro64-rk3399_defconfig b/configs/rockpro64-rk3399_defconfig
index ce1adc53..9fa371c4 100644
--- a/configs/rockpro64-rk3399_defconfig
+++ b/configs/rockpro64-rk3399_defconfig
@@ -14,7 +14,6 @@ CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI=y
 CONFIG_SYS_LOAD_ADDR=0x800800
 CONFIG_DEBUG_UART=y
-CONFIG_USE_PREBOOT=y
 CONFIG_DEFAULT_FDT_FILE="rockchip/rk3399-rockpro64.dtb"
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_MISC_INIT_R=y