regulator: qcom_smd: Add pmi8994 regulator support

The pmi8994 is commonly found on MSM8996 based devices, such as the
Dragonboard 820c, where it supplies power to a number of LDOs on the
primary PMIC.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200324041424.518160-1-bjorn.andersson@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>