arm64: dts: qcom: qrb4210-rb2: Describe fixed regulators

The board hosts a whole lot of fixed regulators. Describe them.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-and-Tested-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230515-topic-rb2-bits-v1-1-a52d154a639d@linaro.org