As we may need to support other physical layers, we can avoid linking the
core part into each and every pn544 module.
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

The driver now has all HCI stuff isolated in one file, and all the
hardware link specifics in another. Writing a pn544 driver on top of
another hardware link is now just a matter of adding a new file for that
new hardware specifics.
Signed-off-by: NEric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>