regulator: Add QCOM SPMI regulator driver

Add an SPMI regulator driver for Qualcomm's PM8841, PM8941, and
PM8916 PMICs. This driver is based largely on code from
codeaurora.org[1].

[1] https://www.codeaurora.org/cgit/quic/la/kernel/msm-3.10/tree/drivers/regulator/qpnp-regulator.c?h=msm-3.10


Cc: David Collins <collinsd@codeaurora.org>
Cc: <devicetree@vger.kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>