dt-bindings: remoteproc: wcnss-pil: Make supplies optionally required

On MSM8974, power domains are not yet supported. The platform uses
regulators. This patch marks either the power-domains or *-supply as
required (instead of always requiring the power domains).

Signed-off-by: Sireesh Kodali <sireeshkodali1@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221001031345.31293-6-sireeshkodali1@gmail.com