Documentation/ABI: Add new attribute for mlxreg-io sysfs interfaces

Add documentation for the new attributes for exposing CPLDs part
numbers and CPLD minor versions.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Documentation/ABI/stable/sysfs-driver-mlxreg-io

@@ -206,3 +206,20 @@ Description:	This file exposes the firmware version of burnable voltage
 		regulator devices.
 
 		The file is read only.
+
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld1_pn
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld2_pn
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld3_pn
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld4_pn
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld1_version_min
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld2_version_min
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld3_version_min
+What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/cpld4_version_min
+Date:		July 2020
+KernelVersion:	5.9
+Contact:	Vadim Pasternak <vadimpmellanox.com>
+Description:	These files show with which CPLD part numbers and minor
+		versions have been burned CPLD devices equipped on a
+		system.
+
+		The files are read only.