regulator: qcom-smd: Add PM8916 support

This patch adds support and documentation for the PM8916 regulators
found on MSM8916 platforms.

Acked-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Andy Gross <agross@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>