Improve Logging

[asensio-project]

Hello,

This PR improves the actual logging of the bootloader.

Tasks:

• Separate the logger from the framebuffer
• Add support for Serial Being logger
• Add configurations for enabling or disabling these methods of logging

Closes #306

Thanks!

[phil-opp]

Looks great already, thanks a lot! The serial printing seems to work already on the CI, for example we see the bootloader output here: /~https://github.com/rust-osdev/bootloader/actions/runs/3846887378/jobs/6552698281#step:11:223

Just for information: I just restarted the Windows CI job manually in the hope of triggering the timeout issue e.g. seen in #304. I suspect that the cause of that timeout could be a panic in the bootloader, which this PR should make visible.

[jasoncouture]

Makes sense. I'll also block config.txt on this as well, once the kernel config is in place.
It may yet again be wise to wait on #302 to avoid conflicts before doing the kernel config. So, perhaps do what is currently in this PR separately, as it'll be a huge help.

[phil-opp]

Looks very good! I only left some style comments.

[asensio-project]

I can't apply the changes proposed by @jasoncouture in the linked issue because it's very difficult to refactor BIOS stages due incompatibility problems of the used crates of the logger. So, I think that this PR is ready to merge.

[phil-opp]

Thanks!