entropy: outsource code

entropy: outsource code

This patch ought to be small and simple ...

The reason why it's not is me wanting the entropy data out of struct
information. This means update_entropy() can not be used anymore, as it
uses this globally available object.

The solution I am presenting here is quite messy regarding header
includes. Hopefully this will go away soon as I plan on creating some
sort of "OS library" containing all OS specific routines and defining
macros for easier capability checking in the non-specific code. This on
the other hand means we'll need "wrappers" around OS specific objects,
but that's not as bad as it seems - having non-specific text objects
only will definitely clean up the code, and capabilities can be checked
where they should be.