dt-bindings: iio: adc: ad7192: Update clock config

dt-bindings: iio: adc: ad7192: Update clock config

There are actually 4 configuration modes of clock source for AD719X
devices. Either a crystal can be attached externally between MCLK1 and
MCLK2 pins, or an external CMOS-compatible clock can drive the MCLK2
pin. The other 2 modes make use of the 4.92MHz internal clock.

To configure external clock as either a crystal or a CMOS-compatible
clock, changing the register settings is necessary. Therefore, add clock
name xtal alongside mclk. By selecting one or the other, the register is
configured.

The presence of an external clock source is optional, not required. When
both clocks and clock-names properties are present, an external clock
source is used. If the intention is to use the internal clock, both
properties should be absent. Modify required properties accordingly.

Signed-off-by: Alisa-Dariana Roman <alisa.roman@analog.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20240717212535.8348-2-alisa.roman@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>