package/libnfc: add sub-options to enable individual drivers

package/libnfc: add sub-options to enable individual drivers

Until now, the arygon and pn53x_usb were unconditionally enabled, and
there were no options to choose other drivers. Therefore, we had
sub-options for each individual driver, keeping arygon and pn53x_usb
enabled by default to preserve backward compatibility.

Also, due to this, the BR2_TOOLCHAIN_HAS_THREADS dependency on the
libnfc package is no longer needed, and is only needed for some of the
sub-options.

Signed-off-by: Louis Aussedat <aussedat.louis@gmail.com>
[Thomas:
 - drop the default ""
 - remove the top-level HAS_THREADS dependency, and move it down to
   the sub-options that need it
 - improve commit log]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>