mfd: qcom-rpm: Add support for pm8018 RPM Regulator

In order to support the Qualcomm MDM9615 SoC, add support for the
RPM regulator entries in the qcom-rpm driver.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>