sysfs: export function to reenumerate all devfs/sysfs interfaces

[maruel]

Then if a user do something that she knows is doing to expose more interfaces, like using config-pin then the user will want periph to realize that without having to restart the app.

Thinking about signature sysfs.Reenumerate() error

[maruel]

There's an interesting issue with this, in the case of CPU memory mapped pins, as the CPU driver may have overridden the pins.

[maruel]

Ported to https://github.com/periph/host/issues/43.