hwmon: (ina2xx) Use structure array to distinguish chip types

Replace per-device initialization and per-device calculation code with
per-device configuration data, which is then used to configure the chip and
perform calculations based on that data.

This patch reduces code size by more than 400 bytes on x86_64.

Cc: Lothar Felten <l-felten@ti.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jean Delvare <khali@linux-fr.org>