[examples] Add Gemmini-baremetal examples and more conv2d examples.

[shirohasuki]

1. Add Gemmini-baremetal examples for spike and verilator evaluation.
2. Add more gemmini conv2d operation examples (like conv-2d-nhwc-fhwc).

[zhanghb97]

Giving some quick feedback:

• Missing empty line at the end of the files.
• Please use our pre-commit tools:

$ cd buddy-mlir
$ pip install pre-commit
$ pre-commit install

[zhanghb97]

Have not seen the E2E example.
Is the remaining E2E C++ error ('_start_main_argv') related to using riscv64-unknown-elf-gcc (expecting riscv64-unknown-elf-g++) for end-to-end?

[shirohasuki]

Yes, E2E example still block points at compiling with riscv64-unknown-elf-g++.
I will try to fix it and follow up with a full version commit.

[linuxlonelyeagle]

There are a few nits to note.Finally, thank you for your contribution.

[shirohasuki]

Add pre-commit tools and fix some glitches.