python-spidev: bump to version 3.1

Also add hash file.

And fixes:
http://autobuild.buildroot.net/results/abc/abca38e3e93b609c1040c1152de7cd59940e2c88/


It was using an absolute include_dirs in setup.py pointing to the host
kernel sources (/usr/src/linux). It didn't affect "normal" distros since
they normally don't have the kernel sources installed, however for
Gentoo it's quite normal to have kernel sources there.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>