Dear maintainers,

Here is a series of patches adding support for AD7191, a chip from the AD719X
family, with similar functionalities. Since this chip is entirely
pin-programmable with no registers, I wrote a separate driver from ad7192.c.
Sigma delta adc drivers use the set_mode() callback function which contains a
register write to make sure the chip select line is asserted before waiting for
an interrupt. Devices such as AD7191 and AD7780 have no registers to write to,
so I added a helper function ad_sd_assert_cs() for these use cases.

Kind regards,
Alisa-Dariana Roman.