At the moment only the sync polarity for CRT is handled but there are
also bits for controlling the sync polarity for other output devices.
Add a function to change those similar to the other output device
functions.
There is no runtime change yet as the code still handles only CRT.
Signed-off-by: NFlorian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Joseph Chan <JosephChan@via.com.tw>