dt-bindings: mfd: qcom-spmi-pmic: Document PM8937 PMIC

Add bindings for PM8937 PMIC (qcom,pm8937). This PMIC is found in
boards with MSM8917, MSM8937, MSM8940 and APQ variants.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Dang Huynh <danct12@riseup.net>
Link: https://lore.kernel.org/r/20231121-pm8937-v2-2-b0171ab62075@riseup.net


Signed-off-by: Lee Jones <lee@kernel.org>