NFC: digital: Add NFC-DEP Target-side ATN Support

When an NFC-DEP target receives an ATN PDU, its
supposed to respond with a similar ATN PDU.
When the Target receives an I PDU with the PNI
one less than the current PNI and the last PDU
sent was an ATN PDU, the Target is to resend the
last non-ATN PDU that it has sent.  This is
described in section 14.12.3.4 of the NFC Digital
Protocol Spec.

The digital layer's NFC-DEP code doesn't implement
this so add that support.

Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>