documentation/iommu: Add note on existing DT binding status

The current dt binding for Exynos System MMU can be changed, if found
incompatible with the support for "Generic IOMMU Binding".
This patch adds a note to the binding documentation stating the same.

Signed-off-by: Shaik Ameer Basha <shaik.ameer@samsung.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Documentation/devicetree/bindings/iommu/samsung,sysmmu.txt

@@ -27,6 +27,11 @@ The drivers must consider how to handle those System MMUs. One of the idea is
 to implement child devices or sub-devices which are the client devices of the
 System MMU.
 
+Note:
+The current DT binding for the Exynos System MMU is incomplete.
+The following properties can be removed or changed, if found incompatible with
+the "Generic IOMMU Binding" support for attaching devices to the IOMMU.
+
 Required properties:
 - compatible: Should be "samsung,exynos-sysmmu"
 - reg: A tuple of base address and size of System MMU registers.