NFC: Separate pn544 hci driver in HW dependant and independant parts

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: Eric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>