NFC: digital: Add Inititor-side PSL support

In order to operate at the fasted bit rate
possible, add initiator-side support for
PSL REQ while in P2P mode.  The PSL REQ
will switch the RF technology to 424F
whenever possible.

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>