dt-bindings: opp: Allow opp-supported-hw to contain multiple versions

A single list of versions for a hierarchy of hardware levels is not
sufficient in some cases. For example, if the hardware version has two
levels, i.e. X.Y and we want an OPP to support only version 2.1 and 1.2,
we will set the property as:

	opp-supported-hw = <0x00000003 0x00000003>;

What this also does is enable hardware versions 2.2 and 1.1, which we
don't want.

Extend the property to accept multiple versions, so we can define the
property as:

	opp-supported-hw = <0x00000002 0x00000001>, <0x00000001 0x00000002>;

While at it, also reword the property description.

Reported-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>