iio: dac: adding support for Microchip MCP47FEB02

iio: dac: adding support for Microchip MCP47FEB02

This is the iio driver for Microchip MCP47F(E/V)B(0/1/2)1,
MCP47F(E/V)B(0/1/2)2, MCP47F(E/V)B(0/1/2)4 and MCP47F(E/V)B(0/1/2)8 series
of buffered voltage output Digital-to-Analog Converters with nonvolatile or
volatile memory and an I2C Interface.

The families support up to 8 output channels.

The devices can be 8-bit, 10-bit and 12-bit.

Signed-off-by: Ariana Lazar <ariana.lazar@microchip.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>