* misc: cleanup for submodules and Makefile

* misc: use ready-to-run submodule
Co-authored-by: NWilliam Wang <zeweiwang@outlook.com>

* Recover Ftq Pointer and send miss req to I$ MSHRs
* Instruction reorder is done by Ftq

* TODO: need a solution for fetch-on-miss

difftest: support --no-diff arg to emulate without difftest by nemu

* Difftest should always be instantiated even if "--no-diff" is enabled
* cuz we need in-core info to implement some arguments like "--max-instr" by DPI-C.
* Therefore, instantiation of difftest and nemu-proxy is decoupled.

* Add ZH-Hans readme.md and fix some grammar issues in english readme
Signed-off-by: NClSlaid <cailue@bupt.edu.cn>

* Typo fixes in ZH-Hans.md
Signed-off-by: NClSlaid <cailue@bupt.edu.cn>

* Add link to zh-hans in readme
Signed-off-by: NClSlaid <cailue@bupt.edu.cn>

* build.sc: remove `testOnly`

mill 0.98 added its own `testOnly`. If we keep our version, we can't compile build.sc.
Some people in the WeChat tutorial group have already encountered this issue.

* Pin mill version to 0.9.8

https://github.com/OpenXiangShan/XiangShan/pull/843#issuecomment-868669873