package/libsigrok: add optional bluez-utils dependency

bluez-utils has been added since version 0.5.2 and
https://github.com/sigrokproject/libsigrok/commit/f085705f4888f8127c80539e0fcd1cb3974bdff2



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