drivers/iio/frequency/cf_axi_dds: add support for DAC_DP_DISABLE

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
drivers/iio/adc/cf_axi_adc: add support for ADC_DP_DISABLE

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>