crate: transfer embedded-hal-sdmmc ownership

[rmsyn]

I've created the embedded-hal-sdmmc as an experimental crate for eventual upstreaming into the embedded-hal workspace.

The current home for the embedded-hal-sdmmc crate is on codeberg.

The original PR for the crate started rust-embedded/embedded-hal#662.

As part of proving/developing the traits, I opened another PR for SDIO trait implementation in esp-hal.

@bugadani suggested creating an experimental crate, and further discussion with the rust-embedded WG led to the crate creation.

As part of the stabilization process, I would like to transfer ownership of the crate to the rust-embedded-community organization after the crate is out of alpha-stage development.

These traits should also prove useful as a basis for non-SPI implementations of the embedded-sdmmc-rs driver. The current SPI implementation should also be possible to port to the embedded-hal-sdmmc traits.

Related: #6

[eldruin]

Sounds good to me, thanks!
Please have a look here and let me know how you want to proceed.