doc: Fix output of version string when using Sphinx with Python 3
doc: Fix output of version string when using Sphinx with Python 3

Our Sphinx configuration gets the current skiboot version by using the
subprocess module to run make_version.sh. In Python 2, this returns a
value of type str, but in Python 3, this returns bytes instead.

Decode those bytes into a string so we see "skiboot 5.6.blah" rather
than "skiboot b'5.6.blah\n'" in the documentation output.

Tested using Sphinx with both Python 2 and 3.

Signed-off-by: Andrew Donnellan <efc2d7c347a094a6ec1d918179e819039044c564@au1.ibm.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

legoater/skiboot,legoater/skiboot,qemu/skiboot,open-power/skiboot,shenki/skiboot,stewart-ibm/skiboot,shenki/skiboot,qemu/skiboot,qemu/skiboot,mikey/skiboot,stewart-ibm/skiboot,shenki/skiboot,open-power/skiboot,open-power/skiboot,legoater/skiboot,legoater/skiboot,qemu/skiboot,stewart-ibm/skiboot,mikey/skiboot,shenki/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,open-power/skiboot,mikey/skiboot,qemu/skiboot