dt-bindings: mfd: qcom,spmi-pmic: Add nvram function

Add an 'nvram' pattern property and a reference to the corresponding
SDAM DT schema.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230320135710.1989-4-johan+linaro@kernel.org