Other functions in the VT82xx chips need to raise ISA interrupts. Keep
a reference to them in the device state and add via_isa_set_irq() to
allow setting their state.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <778c04dc2c8affac060b8edf9e8d7dab3c3e04eb.1634259980.git.balaton@eik.bme.hu>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>