package/pinentry: add pinentry-fltk

pinentry-fltk has been added in version 1.1.0 with
https://github.com/gpg/pinentry/commit/6c45eed62214b44fcc11e642b19df7b6ca0da0bd



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>