package/cryptsetup: add libnss support

libnss is a crypto backend since version 1.3.0 and
https://github.com/mbroz/cryptsetup/commit/7b6eda0d273eb514bf2c1f834a5af019f614f606



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