dt-bindings: cpufreq: Convert ti-cpufreq to json schema

Move the ti-cpufreq binding over to opp and convert the free text
binding to json-schema.

Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>