msm: Add rpm-regulator-smd driver to support RPM regulators over SMD

The rpm-regulator-smd driver makes use of a key based RPM
resource interface in order to control regulators.  Regulator
requests are sent to the RPM over the SMD transport layer.

Provide control of regulators in both the active and sleep sets.
Active set regulator requests take effect immediately.  Sleep set
requests take effect when the Apps processor transitions into
RPM assisted power collapse.

Allow for all request parameters to be initialized based upon
configuration data specified in device tree.

Include an API which allows for regulator control from atomic
context in order to support all consumer use cases.

Change-Id: I0417d52bba9eb053b6c552b287aa658d6c8e4b7f
Signed-off-by: David Collins <collinsd@codeaurora.org>