regulator: Add qpnp-regulator driver

Add the qpnp-regulator driver to support regulators found in
Qualcomm plug-and-play (QPNP) PMIC chips.  QPNP chips make use of
Qualcomm's SPMI register convention.  The particular hardware
characteristics of a given regulator can be derived from the
values present in the type and subtype registers.

The qpnp-regulator driver supports probing with either device tree
device specification or with board file specified platform data.

Change-Id: I4f74431a50949763d651faf992b5d2567d05758e
Signed-off-by: David Collins <collinsd@codeaurora.org>
[sboyd: Squash in DT binding document]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>