sm501: Implement i2c part for reading monitor EDID

Emulate the i2c part of SM501 which is used to access the EDID info
from a monitor.

The vmstate structure is changed and its version is increased but
SM501 is only used on SH and PPC sam460ex machines that don't support
cross-version migration.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>