mos6522: add "info via" HMP command for debugging

mos6522: add "info via" HMP command for debugging

This displays detailed information about the device registers and timers to aid
debugging problems with timers and interrupts.

Currently the QAPI generators for HumanReadableText don't work correctly if
used in qapi/target-misc.json when a non-specified target is built, so for
now manually add a hmp_info_via() wrapper until direct support for per-device
HMP/QMP commands is implemented.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220305150957.5053-9-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>