arm64: dts: qcom: 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.

The change should have no implications on any SM8250 CAMSS users, since
none of the boards supported in upstream enables the camss device tree node.

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