MAINTAINERS: Add the driver info of the NXP IMX8QXP

The NXP i.MX 8QuadXPlus SOC has a new ADC IP. After adding
the driver support for it, I add the driver info of the
NXP IMX8QXP ADC to MAINTAINERS file.

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Link: https://lore.kernel.org/r/20210925020555.129-4-caihuoqing@baidu.com


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