I checkout u-boot tag: v2023.10

https://github.com/u-boot/u-boot/tree/v2023.10

run build:

```shell export STAGING_DIR=/home/foo/openwrt-toolchain-22.03.4-ramips-mt7621_gcc-11.2.0_musl.Linux-x86_64/

make mt7621_rfb_defconfig make CROSS_COMPILE=/home/foo/openwrt-toolchain-22.03.4-ramips-mt7621_gcc-11.2.0_musl.Linux-x86_64/toolchain-mipsel_24kc_gcc-11.2.0_musl/bin/mipsel-openwrt-linux-musl- ```

build failed:

```shell CC spl/common/spl/spl.o AR spl/common/spl/built-in.o LD spl/u-boot-spl OBJCOPY spl/u-boot-spl-nodtb.bin COPY spl/u-boot-spl.bin SYM spl/u-boot-spl.sym MKIMAGE u-boot.img MKIMAGE u-boot-dtb.img LZMA u-boot.bin.lzma MKIMAGE u-boot-lzma.img BINMAN .binman_stamp Image 'u-boot-spl-ddr' is missing external blobs and is non-functional: stage_bin

/binman/u-boot-spl-ddr/stage_bin (mt7621_stage_sram.bin): Missing blob

Some images are invalid make: *** [Makefile:1115: .binman_stamp] Error 103 ```

Is there a step I'm missing that's causing this?