dt-bindings: opp: qcom-nvmem: Make speedbin related properties optional

Not all Qualcomm platforms need to care about the speedbin efuse,
nor the value blown into the speedbin efuse.
Therefore, make the nvmem-cells and opp-supported-hw properties
optional.
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Reviewed-by: Ilia Lin <ilia.lin@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Documentation/devicetree/bindings/opp/qcom-nvmem-cpufreq.txt

@@ -20,6 +20,10 @@ In 'cpus' nodes:
 In 'operating-points-v2' table:
 - compatible: Should be
 	- 'operating-points-v2-kryo-cpu' for apq8096 and msm8996.
+
+Optional properties:
+--------------------
+In 'operating-points-v2' table:
 - nvmem-cells: A phandle pointing to a nvmem-cells node representing the
 		efuse registers that has information about the
 		speedbin that is used to select the right frequency/voltage