Fix location of data

[sosthene-nitrokey]

This is a temporary fix until trussed gives us a way to have a per-backend store of data

[sosthene-nitrokey]

This does mean that the salt is at

/// trussed/
///     dat/
///         backend-auth/
///             salt            global salt for key derivation

[robin-nitrokey]

Should we move it to trussed/backend-auth/dat for consistency?

[sosthene-nitrokey]

Let's move the global state to /backend-auth/dat/.... Trussed will then enforce the backend- prefix in the future

[sosthene-nitrokey]

Current layout:

:: PERSISTENT
/backend-auth p(/)
/backend-auth/dat p(/backend-auth)
/backend-auth/dat/backend-auth p(/backend-auth/dat)
/backend-auth/dat/backend-auth/salt p(/backend-auth/dat/backend-auth)
/test p(/)
/test/backend-auth p(/test)
/test/backend-auth/dat p(/test/backend-auth)
/test/backend-auth/dat/pin.00 p(/test/backend-auth/dat)
/trussed p(/)
/trussed/dat p(/trussed)
/trussed/dat/rng-state.bin p(/trussed/dat)