mos6522: switch over to use qdev gpios for IRQs

mos6522: switch over to use qdev gpios for IRQs

For historical reasons each mos6522 instance implements its own setting and
update of the IFR flag bits using methods exposed by MOS6522DeviceClass. As
of today this is no longer required, and it is now possible to implement
the mos6522 IRQs as standard qdev gpios.

Switch over to use qdev gpios for the mos6522 device and update all instances
accordingly.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220305150957.5053-5-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>