hwmon: (emc1403) Add support for emc14x2

Add support for emc1402/emc1412/emc1422 temperature monitoring chips.
This line of sensors only has 2 temperature channels (internal and external)
in comparison to the emc14x3 (3 channels) and emc14x4 (4 channels).

Signed-off-by: Josef Gajdusek <atx@atx.name>
[Guenter Roeck: ordered i2c address list, updated description/headline]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>