Add a workaround for broken Genius Tablet with partial pressure updates

If you have lines like in bug 342641, please add the following line into
your kritarc:

workaroundX11SmoothPressureSteps=3

After that restart Krita and you'll see a message like:

"WARNING: Workaround for broken tablet pressure reports
 is activated. Number of smeeth steps: 3"

The problem should go after that.

CCBUG:342641