regulator: qcom-smd: Add PM8994 regulator support

This patch adds support for the PM8994 regulators found on msm8992,
msm8994 and msm8996 platforms.

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
[bjorn: Add DT binding doc and vdd_lvs1_2 supply]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>