NFC: pn533: Separate physical layer from the core implementation

The driver now has all core stuff isolated in one file, and all
the hardware link specifics in another. Writing a pn533 driver
on top of another hardware link is now just a matter of adding a
new file for that new hardware specifics.

The first user of this separation will be the i2c based pn532
driver that reuses pn533 core implementation on top of an i2c
layer.

Signed-off-by: Michael Thalmeier <michael.thalmeier@hale.at>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>