Documentation: ABI: testing: admv1014: add ABI docs

Add documentation for the use of the Digital Attenuator gain.
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://lore.kernel.org/r/20220215081216.67706-3-antoniu.miclaus@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio

@@ -476,6 +476,7 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY_i_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY_q_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltage_i_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltage_q_calibscale
+What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltage_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_accel_x_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_accel_y_calibscale

Documentation/ABI/testing/sysfs-bus-iio-frequency-admv1014

+What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0_i_calibscale_coarse
+KernelVersion: 5.18
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Read/write value for the digital attenuator gain (IF_I) with coarse steps.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0_q_calibscale_coarse
+KernelVersion: 5.18
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Read/write value for the digital attenuator gain (IF_Q) with coarse steps.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0_i_calibscale_fine
+KernelVersion: 5.18
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Read/write value for the digital attenuator gain (IF_I) with fine steps.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0_q_calibscale_fine
+KernelVersion: 5.18
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Read/write value for the digital attenuator gain (IF_Q) with fine steps.