migration: Split qemu-file.h

migration: Split qemu-file.h

Split the file into public and internal interfaces.  I have to rename
the external one because we can't have two include files with the same
name in the same directory.  Build system gets confused.  The only
exported functions are the ones that handle basic types.

Signed-off-by: Juan Quintela <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>