generator: make independent methods static
generator: make independent methods static

Most of these functions used to be static functions.
They were turned into "class methods" by isl-0.18-595-gdab674e14c (Turn
python generator into a subclass of generator, Sat Apr 8 05:12:47 2017 +0200),
without a clear motivation.
Since these methods do not require access to any fields, at least make
them static.  Otherwise, any function calling them needs to be turned
into a method of generator as well.

The other functions turned into static methods by this commit
are either similar to the original ones or depend on them.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,PollyLabs/isl,PollyLabs/isl,PollyLabs/isl,Meinersbur/isl,Meinersbur/isl,PollyLabs/isl,PollyLabs/isl