mfd: max14577: Add detection of device type

This patch continues the preparation for adding support for MAX77836
device to existing max14577 driver.

Add enum for types of devices supported by this driver. The device type
will be detected by matching of_device_id, or i2c_device_id as a
fallback.

The patch also moves to separate function the code related to displaying
DeviceID register values.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>