Add serial and PWM subdevice types to `demo/python/info.py`.

Add serial and PWM subdevice types to `demo/python/info.py`.

This catches it up for the folowing commits to the comedi repository:

  commit 311e9c540217d60bdf56a1dba9eafe474fd3b218
  Author: Bernd Porr <Bernd.Porr@f2s.com>
  Date:   Sun Jan 13 23:07:02 2008 +0000

    Added a proper PWM subdevice for comedi.

  commit 8092ed57ff38e1fcaf75a7e0bf3b8c4f5372f3d7
  Author: Frank Mori Hess <fmhess@speakeasy.net>
  Date:   Sat Jan 31 22:13:09 2004 +0000

    serial dio (SCXI) support from Caleb Tennis