dt-bindings: cpufreq: Document operating-points-v2-kryo-cpu

The qcom-cpufreq-kryo driver reads the msm-id and efuse value from the SoC
to provide the OPP framework with required information.
This is used to determine the voltage and frequency value for each OPP of
operating-points-v2 table when it is parsed by the OPP framework.

This change adds documentation for the DT bindings.
The "operating-points-v2-kryo-cpu" DT extends the "operating-points-v2"
with following parameters:
- nvmem-cells (NVMEM area containig the speedbin information)
- opp-supported-hw: A single 32 bit bitmap value,
  representing compatible HW:
			0:	MSM8996 V3, speedbin 0
			1:	MSM8996 V3, speedbin 1
			2:	MSM8996 V3, speedbin 2
			3:	unused
			4:	MSM8996 SG, speedbin 0
			5:	MSM8996 SG, speedbin 1
			6:	MSM8996 SG, speedbin 2
			7-31:	unused

Signed-off-by: Ilia Lin <ilialin@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Tested-by: Amit Kucheria <amit.kucheria@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>