Some parts of python3.mk were hardcoding the 3.3 version as the major
version, which does not work for Python 3.4 and other future
versions. Instead, use the existing PYTHON3_VERSION_MAJOR.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>