bump u-boot version

[BradWalker]

There is an issue with the version of U-Boot in the repo for this project.

In particular, the RISC-V ISA has separated the ZICSR and ZIFENCEI from the base and into their own extension, chapter 3 & chapter 9.
https://riscv.org/wp-content/uploads/2019/06/riscv-spec.pdf
This also means current released compilers like riscv64-linux-gnu-gcc will not support these instructions.

This is the issue that I'm hitting.

As a result, the U-Boot team cleaned up their Makefile to support adding these instructions as extensions to gcc. The change was implemented in this commit.
u-boot/u-boot@1dde977

The easiest thing would be to bump the version referenced in the project to the tag v2023.01 . I've tested this out and it works correctly.

I hope this is possible.

[eugene-tarassov]

I tried to upgrade u-boot to 2023.1 and it did not work, too many issues. Some of them I don't know how to resolve. Eventually I will figure it out. Meantime, I suggest to use Ubuntu 20.04.6 LTS as the development environment, as recommended by the README. It is well tested and works fine.