Bump nemu ref in ready-to-run

[NewPaulWalker]

• NEMU commit: https://github.com/OpenXiangShan/NEMU/pull/573
• NEMU configs:
  • riscv64-xs-ref_defconfig
  • riscv64-dual-xs-ref_defconfig

Including:

• refactor(csrrw): rewrite csr read/write using switch-case instead of multiple if-else.

[NewPaulWalker]

After tested OK, I will rewrite commit info and rebase to master. Before that, I want to use this pr commit to test XiangShan CI.