python-pyzmq: enable PyZMQ for Python 3

The PyZMQ package is currently limited to Python 2; however, its
build system does not require the Python 2 interpreter and will work
as is with Python 3 (tested).

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>