mlxsw: documentation: Add resources ABI documentation

Add resources ABI documentation.
Signed-off-by: NArkadi Sharhsevsky <arkadis@mellanox.com>
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/ABI/testing/devlink-resource-mlxsw

+What: 		/kvd/
+Date:		08-Jan-2018
+KernelVersion:	v4.16
+Contact:	mlxsw@mellanox.com
+Description:	The main database in the Spectrum device is a centralized
+		KVD database used for many of the tables used to configure
+		the chip including L2 FDB, L3 LPM, ECMP and more. The KVD
+		is divided into two sections, the first is hash-based table
+		and the second is a linear access table. The division
+		between the linear and hash-based sections is static and
+		require reload before the changes take effect.
+
+What: 		/kvd/linear
+Date:		08-Jan-2018
+KernelVersion:	v4.16
+Contact:	mlxsw@mellanox.com
+Description:	The linear section of the KVD is managed by software as a
+		flat memory accessed using an index.
+
+What: 		/kvd/hash_single
+Date:		08-Jan-2018
+KernelVersion:	v4.16
+Contact:	mlxsw@mellanox.com
+Description:	The hash based section of the KVD is managed by the switch
+		device. Used in case the key size is smaller or equal to
+		64bit.
+
+What: 		/kvd/hash_double
+Date:		08-Jan-2018
+KernelVersion:	v4.16
+Contact:	mlxsw@mellanox.com
+Description:	The hash based section of the KVD is managed by the switch
+		device. Used in case the key is larger than 64 bit.