ADT7481, ADT7482, and ADT7483 are similar to ADT7461, but support two
external temperature sensors, similar to MAX6695/6696. They support an
extended temperature range similar to ADT7461. Registers for the second
external channel can be accessed directly or by using the same method as
used by MAX6695/6696. For simplicity, the access method implemented for
MAX6695/6696 is used.

The chips support PEC (packet error checking). Set the PEC feature flag
and let the user decide if it should be enabled or not (it is by default
disabled).

Even though it is only documented for ADT7483, all three chips support a
secondary manufacturer ID register at 0x3e and a chip ID register at 0x3f.
Use the contents of those registers register for improved chip detection
accuracy. Add the same check to the ADT7461A detection code since this chip
also supports the same (undocumented) registers.

Devicetree nodes are not added for the added chips since it is quite
unlikely that such old chips will ever be used in a devicetree based
system. They can be added later if needed.
Reviewed-by: Slawomir Stepien <sst@poczta.fm>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>