Allow uefi-services to work when the "logger" feature is disabled in uefi

[NathanRoyer]

Hello! We are using these crates in our project (Theseus OS), and we would like to use uefi without the logger feature.
However, I discovered that the uefi-services crate forces us to have the logger feature enabled in uefi, as per its manifest.

Due to how the log crate is implemented, it is impossible to set a logger twice; because uefi-services sets the default one up (and disables it when boot services are exited), we can't set our own logger up.

This PR simply adds a logger feature to uefi-services, which propagates to the same feature in uefi. This allows us to use both crates without the built-in logger.

[nicholasbishop]

Thanks for the PR, code changes LGTM. Could you also add an entry to the uefi-services section of CHANGELOG.md?

[NathanRoyer]

Thanks for the PR, code changes LGTM. Could you also add an entry to the uefi-services section of CHANGELOG.md?

Absolutely

[nicholasbishop]

Thanks!

[phip1611]

However, I discovered that the uefi-services crate forces us to have the logger feature enabled in uefi, as per its manifest.

Not a general recommendation, but I've always seen uefi-services as a template. In almost all my projects, I never used it directly, as it was too limiting from time to time.

I used its code as a base to write my own global allocator and also the other stuff.