Integrate u-boot-seco-rk/niccolor/px30-stop-using-kernel-dtb

Commit: https://git.seco.com/edgehog/bsp/rockchip/u-boot-seco-rk/-/commit/3f0187cc257237b0d6d18ab5ecf70e64c7fb7eba

[PX30][DEFCONFIG] Stop using kernel dtb in u-boot

Up to now, u-boot was using kernel dtb. Now u-boot will use its own dtb, causing an increase of u-boot image size. Need to increase the u-boot size from default 1024 to 2048

Also allign bootdelay to 3sec (as it's for other boards)