media: dt-bindings: media: sm8250-camss: Add power-domain-names property

QCOM SM8250 camera subsystem depends on three power domains, at the moment
all of them are not differentiated one from another, however the power
domains compose a hierarchical structure with vfe0 and vfe1 as subdomains
of titan_top, also managing vfe0 and vfe1 separately allows to get more
fine-grained power control in runtime.

Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>