dt-bindings: iio: adc: hx711: clean up existing binding text

dt-bindings: iio: adc: hx711: clean up existing binding text

Rewrite the binding description and property text so it describes the
existing HX711 hardware behavior directly instead of documenting old
driver implementation details.

Also clarify that clock-frequency controls the SCK bit-bang timing.

No functional change.

Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>