iio:ABI docs: Fix up duplicate *_calibbias_* documentation for icm42600

This device has the unusual characteristic that the calibbias values
have well defined units (more commonly they are tweaks to a DAC)
Unfortunately the previous approach of having more specific documentation
in sysfs-bus-iio-icm42600 results in warnings during the documentation
build and random ordering in the resulting documentation.

To avoid this, add a note to the main documentation on this special
characteristic for the icm42600.   The _available for calibbias was
missing from the main sysfs-bus-iio docs so also add that, allowing
us to drop the icm42600 specific file.

Fixes
$ scripts/get_abi.pl validate warning:
Warning: /sys/bus/iio/devices/iio:deviceX/in_accel_x_calibbias is defined 2 times:  ./Documentation/ABI/testing/sysfs-bus-iio-icm42600:0  ./Documentation/ABI/testing/sysfs-bus-iio:394
Warning: /sys/bus/iio/devices/iio:deviceX/in_accel_y_calibbias is defined 2 times:  ./Documentation/ABI/testing/sysfs-bus-iio-icm42600:1  ./Documentation/ABI/testing/sysfs-bus-iio:395
Warning: /sys/bus/iio/devices/iio:deviceX/in_accel_z_calibbias is defined 2 times:  ./Documentation/ABI/testing/sysfs-bus-iio-icm42600:2  ./Documentation/ABI/testing/sysfs-bus-iio:396
Warning: /sys/bus/iio/devices/iio:deviceX/in_anglvel_x_calibbias is defined 2 times:  ./Documentation/ABI/testing/sysfs-bus-iio-icm42600:3  ./Documentation/ABI/testing/sysfs-bus-iio:397
Warning: /sys/bus/iio/devices/iio:deviceX/in_anglvel_y_calibbias is defined 2 times:  ./Documentation/ABI/testing/sysfs-bus-iio-icm42600:4  ./Documentation/ABI/testing/sysfs-bus-iio:398
Warning: /sys/bus/iio/devices/iio:deviceX/in_anglvel_z_calibbias is defined 2 times:  ./Documentation/ABI/testing/sysfs-bus-iio-icm42600:5  ./Documentation/ABI/testing/sysfs-bus-iio:399

Cc: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Reported-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20210117153816.696693-2-jic23@kernel.org

Documentation/ABI/testing/sysfs-bus-iio

@@ -455,6 +455,19 @@ Contact:	linux-iio@vger.kernel.org
 Description:
 		Hardware applied calibration offset (assumed to fix production
 		inaccuracies).
+		icm42600: For this device values are real physical offsets
+		expressed in SI units (m/s^2 for accelerometers and rad/s
+		for gyroscope)/
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_accel_calibbias_available
+What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_calibbias_available
+KernelVersion:  5.8
+Contact:        linux-iio@vger.kernel.org
+Description:
+		Available values of calibbias. Maybe expressed as either of:
+
+		- a small discrete set of values like "0 2 4 6 8"
+		- a range specified as "[min step max]"
 
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY_calibscale
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY_supply_calibscale

Documentation/ABI/testing/sysfs-bus-iio-icm42600

-What:		/sys/bus/iio/devices/iio:deviceX/in_accel_x_calibbias
-What:		/sys/bus/iio/devices/iio:deviceX/in_accel_y_calibbias
-What:		/sys/bus/iio/devices/iio:deviceX/in_accel_z_calibbias
-What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_x_calibbias
-What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_y_calibbias
-What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_z_calibbias
-KernelVersion:  5.8
-Contact:        linux-iio@vger.kernel.org
-Description:
-		Hardware applied calibration offset (assumed to fix production
-		inaccuracies). Values represent a real physical offset expressed
-		in SI units (m/s^2 for accelerometer and rad/s for gyroscope).
-
-What:		/sys/bus/iio/devices/iio:deviceX/in_accel_calibbias_available
-What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_calibbias_available
-KernelVersion:  5.8
-Contact:        linux-iio@vger.kernel.org
-Description:
-		Range of available values for hardware offset. Values in SI
-		units (m/s^2 for accelerometer and rad/s for gyroscope).