dt-bindings: memory-controllers: exynos5422-dmc: Add interrupt mode

Add description for optional interrupt lines. It provides a new
operation mode, which uses internal performance counters interrupt when
overflow.  This is more reliable than using default polling mode
implemented in devfreq.

Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Documentation/devicetree/bindings/memory-controllers/exynos5422-dmc.txt

@@ -31,6 +31,14 @@ Required properties for DMC device for Exynos5422:
 	The register offsets are in the driver code and specyfic for this SoC
 	type.
 
+Optional properties for DMC device for Exynos5422:
+- interrupt-parent : The parent interrupt controller.
+- interrupts : Contains the IRQ line numbers for the DMC internal performance
+  event counters in DREX0 and DREX1 channels. Align with specification of the
+  interrupt line(s) in the interrupt-parent controller.
+- interrupt-names : IRQ names "drex_0" and "drex_1", the order should be the
+  same as in the 'interrupts' list above.
+
 Example:
 
 	ppmu_dmc0_0: ppmu@10d00000 {
@@ -70,4 +78,7 @@ Example:
 		device-handle = <&samsung_K3QF2F20DB>;
 		vdd-supply = <&buck1_reg>;
 		samsung,syscon-clk = <&clock>;
+		interrupt-parent = <&combiner>;
+		interrupts = <16 0>, <16 1>;
+		interrupt-names = "drex_0", "drex_1";
 	};