dt-bindings: power: Clarify performance capabilities of power-domains

dt-bindings: power: Clarify performance capabilities of power-domains

The power-domains bindings has in many years been used to describe so
called performance-domains too. Rather than using a separate binding it has
been convenient to re-use the power-domain bindings, as in some cases it's
in fact a combination of the both that would be the best description.

Therefore, let's make it more clear that the power-domains bindings can be
used to describe a performance-domain too.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Kevin Hilman <khilman@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230825112633.236607-11-ulf.hansson@linaro.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>