Clean up libftdi dependencies

[maksymko]

This removes dependency on libftdi/libftdi1 include file from mpsse.h

The user still needs to know which library to link against, but issue is left for some other time.

[l29ah]

I don't really understand why is it a good idea to remove the dependency from the header file. Aren't you supposed to have both libraries installed when you build the target application anyway?

[maksymko]

This removes the dependency on config.h, which only exists when you are building the library.
This also removed source code dependency on libftdi header. The problem was that you pick libftdi vs libftdi1, when you compile libmpsse library, not when you compile your target application. However, your target application still implicitly chooses which header to include (ibftdti1 or libftdi), which may cause problems.

As I've mentioned, this solution is still not perfect, because you indeed still need to know which library to link against, but this is a step in the right direction. Alternatively, you can generate mpsse.h header, so that it will include the header from the library, which was used, when libmpsse was compiled.

[Matheus-Garbelini]

Hi @maksymko and @l29ah I've made a PR which ships a static build of libftdi so it works straight away by linking against it.
The generated libmpsse.a includes libftdi, libusb and libconfuse-2.5. Only thing left to do for the user is to link with pthreads and udev and include the header files on src folder. Let me know your feedback.

Regards.