vt82c686: QOM-ify superio related functionality

vt82c686: QOM-ify superio related functionality

Collect superio functionality and its controlling config registers
handling in an abstract VIA_SUPERIO class that is a subclass of
ISA_SUPERIO and put vt82c686b specific parts in a subclass of this
abstract class.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <fbcc8cc8baf83f327612a1ef1c14bcbcdb0e7edb.1616680239.git.balaton@eik.bme.hu>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>