regulator: qcom_rpm-regulator: Add support for pm8018 rpm regulator

In order to support the Qualcomm MDM9615 SoC, add support for the
PM8018 RPM regulator in the qcom_rpm-regulator driver.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>