dt-bindings: opp: Convert to DT schema

Convert the OPP v1 and v2 bindings to DT schema format. As the OPPv2 binding
can be extended by vendors, we need to split the common part out from the
"operating-points-v2" conforming compatible.

Cc: Yangtao Li <tiny.windzz@gmail.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Chen-Yu Tsai <wens@csie.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>