Remove 'static bound requirement on DMA buffers?

[MabezDev]

To be 100% safe, buffers used with the embedded-dma traits must be static. This is because core::mem::forget is safe in Rust, and if a user were to forget a driver whilst a DMA transaction was occurring, the buffer could go out of scope and UB would occur. Not good.

The issue is, is that 'static bounds are a pain to work with, and I think in practice it's unlikely for users to forget our drivers. I think it might be a good idea to have a trade-off here, to remove the 'static bounds to make the drivers easier to use. We can document each driver, and even have a section in our top level docs mentioning our drivers are not leak (forget) safe and must be dropped properly or manually stopped before forgeting.

[MabezDev]

When we look into this, we should also fix #954 as removing the 'static bound will make it more likely that the buffer could be in cache (which the DMA can't write to).

[bjoernQ]

Maybe we should have our own type for buffers which implements Drop and suggest to deny https://rust-lang.github.io/rust-clippy/v0.0.212/index.html#mem_forget

I haven't tried it - just an idea after sleeping over this