iio: adc: Support ROHM BD79124 ADC

The ROHM BD79124 is a 12-bit, 8-channel, SAR ADC. The ADC supports
an automatic measurement mode, with an alarm interrupt for out-of-window
measurements. The window is configurable for each channel.

The I2C protocol for manual start of the measurement and data reading is
somewhat peculiar. It requires the master to do clock stretching after
sending the I2C slave-address until the slave has captured the data.
Needless to say this is not well suopported by the I2C controllers.

Thus do not support the BD79124's manual measurement mode but implement
the measurements using automatic measurement mode, relying on the
BD79124's ability of storing latest measurements into register.

Support also configuring the threshold events for detecting the
out-of-window events.

The BD79124 keeps asserting IRQ for as long as the measured voltage is
out of the configured window. Thus, prevent the user-space from choking
on the events and mask the received event for a fixed duration (1 second)
when an event is handled.

The ADC input pins can be also configured as general purpose outputs.
Make those pins which don't have corresponding ADC channel node in the
device-tree controllable as GPO.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/ca3886c9abcb268ca976e62cd7da28bf5d6e6382.1742560649.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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