[TODO] Refactor of the repo

To support more SoC in a more convenient way, it is better to learn from stm32-rs. My goal is to organize the repo into the following structure:

```
svd
  | peripherals/**.yaml         # peripherals like uart, twi, etc.
  | <soc>_unofficial.yaml       # yaml for patching
  | <soc>_unofficial.svd        # patched yaml
<soc>-pac/                      # crates' meta and generated codes
```