Add dcsr support

[KushalMeghani1644]

This PR adds support for the dcsr (Debug Control and Status Register) CSR.

Changes:

• Added dcsr.rs under src/register/
• Exposed it in register.rs

This addresses issue #1

[romancardenas]

Thanks for your contribution! Please, find my comments attached.

[romancardenas]

Same here: please, do NOT remove anything from the riscv/riscv/CHANGELONG.md file. This file is essential to keep track of changes in the crate across releases. Please, only add on the top (on the [Unreleased] tag) your new contributions.

[KushalMeghani1644]

I hope the changes I have made for the CHANGELOG.md are fine now. If there are still problems I will be happy to fix them.

[romancardenas]

Hey @KushalMeghani1644 take a look at the changes in your PR: https://github.com/rust-embedded/riscv/pull/342/files

Notice that changelog files are wrong; you included a file at the root of the directory of this repo that is not required. Also, you almost removed all the content in the changelog file inside the riscv subfolder. This is against the purpose of changelog files, which are supposed to be a timeline of the changes across time.

Please, try to be careful with these changes, and address the comments reviewers included in previous reviews. Our time is limited, and we really appreciate it if contributors make our lives a little bit easier.

[romancardenas]

As an example of good practices, look at this PR: https://github.com/rust-embedded/riscv/pull/343/files

• Only two commits (1st for first contribution, 2nd for addressing review)
• Very small changes in the changelog file: just adding what is new

We expect something like this to enable the actual review of the contribution.

[KushalMeghani1644]

Hey @romancardenas I am sorry for the inconvenience regarding the CHANGELOG.md, thanks for putting time into my PR. This time I have only kept the CHANGELOG.md with reference to the PR you pointed out (https://github.com/rust-embedded/riscv/pull/343/files) inside the subfolder. And have removed the unnecessary CHANGELOG.md that was at the root of the folder. I hope the changes I made this time are fine.