dt-bindings: memory: tegra30: emc: Document OPP table and voltage regulator

Document new OPP table and voltage regulator properties which are needed
for supporting dynamic voltage-frequency scaling of the memory controller.
Some boards may have a fixed core voltage regulator, hence it's optional
because frequency scaling still may be desired.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201104164923.21238-12-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Documentation/devicetree/bindings/memory-controllers/nvidia,tegra30-emc.yaml

@@ -39,6 +39,15 @@ properties:
     description:
       Phandle of the Memory Controller node.
 
+  core-supply:
+    description:
+      Phandle of voltage regulator of the SoC "core" power domain.
+
+  operating-points-v2:
+    description:
+      Should contain freqs and voltages and opp-supported-hw property, which
+      is a bitfield indicating SoC speedo ID mask.
+
 patternProperties:
   "^emc-timings-[0-9]+$":
     type: object
@@ -218,6 +227,7 @@ required:
   - clocks
   - nvidia,memory-controller
   - "#interconnect-cells"
+  - operating-points-v2
 
 additionalProperties: false
 
@@ -230,6 +240,8 @@ examples:
         clocks = <&tegra_car 57>;
 
         nvidia,memory-controller = <&mc>;
+        operating-points-v2 = <&dvfs_opp_table>;
+        core-supply = <&vdd_core>;
 
         #interconnect-cells = <0>;