iio: adc: ad4170-4: Add support for buffered data capture

Extend the AD4170-4 driver to allow buffered data capture in continuous
read mode. In continuous read mode, the chip skips the instruction phase
and outputs just ADC sample data, enabling faster sample rates to be
reached. The internal channel sequencer always starts sampling from channel
0 and channel 0 must be enabled if more than one channel is selected for
data capture. The scan mask validation callback checks if the
aforementioned condition is met.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://patch.msgid.link/10ed544d31aa86eb40f93ea947f151d3d9827952.1751895245.git.marcelo.schmitt@analog.com


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