package/python-matplotlib: add kiwisolver dependency

This is needed by matplotlib.pyplot, and is also documented at
https://matplotlib.org/users/installing.html#building-on-linux



Signed-off-by: Esben Haabendal <esben@geanix.com>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>