Add a platform abstraction layer to be able to add a whole different
platform like NALLINO.

The current implementation was based on the Flash-N-Go Boot and the
previous Linux implementation for the Garz & Fricke SAN* platforms.

This however does not fit into for the NALLINO board and thus we need
new function for the new board. To be able to add a new platform
introduce the struct gfplatdetect_platform that abstracts platform
specific read function of the PFID pins and their evaluation.

Many refactoring changes were made to make the code more readable and
better structured.

Right now the NALLINO/iMX6ULL is not yet implemented.