iio: adc: adding support for MCP3564 ADC

This is the iio driver for Microchip family of 153.6 ksps,
Low-Noise 16/24-Bit Delta-Sigma ADCs with an SPI interface
(Microchip's  MCP3461, MCP3462, MCP3464, MCP3461R, MCP3462R,
MCP3464R, MCP3561, MCP3562, MCP3564, MCP3561R,
MCP3562R and MCP3564R analog to digital converters).

Signed-off-by: Marius Cristea <marius.cristea@microchip.com>
Link: https://lore.kernel.org/r/20230829154133.40716-3-marius.cristea@microchip.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>