Implement MCI emulation for native

[x3ro]

The MSBA2 has an MCI driver to talk to the on-board
SD-card reader, but until now there was no way of
running/testing an application using it under native.
This PR adds rudimentary emulation of the MCI interface
and provides a test application.

[miri64]

Would be cool if you can actually store to a file instead of an array :-)

[x3ro]

@authmillenon This is just the low-level interface for talking to the storage medium. Everything else will be built on top of that, but I need this for testing :)

[miri64]

Maybe I miss something, but cpu/native/mci/native-mci.c looks pretty much like an implementation and not like an interface for me. ;-) I meant, that you could store everything you throw in there into a file (with a fixed filename and size, e.g. cpu/native/mci8388608.dat), instead of the array native_mci_memory. Would also be far less RAM hungry ;-).

[x3ro]

Oh :) Yeah, I misunderstood you there. Why would you want to store a file? That is, what would be your use case?

[miri64]

The MCI interface is used for persistent data, right? A file is persistent. An array in RAM not.

[miri64]

+ the module would block less RAM. And yes, when you start to use 8MB for one module I get grumpy, even on native ^^.

[LudwigKnuepfer]

I already wrote a file based storage driver for native for some other interface.

[LudwigKnuepfer]

#2239

[x3ro]

@authmillenon Updated to use a file instead of RAM ✨

[miri64]

💃

[miri64]

Superseded by #4345