iio: imx8qxp-adc: Add driver support for NXP IMX8QXP ADC

The NXP i.MX 8QuadXPlus SOC has a new ADC IP, so add
driver support for this ADC.

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210925020555.129-2-caihuoqing@baidu.com


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