regulator: Regulator driver for the Qualcomm RPM

Driver for regulators exposed by the Resource Power Manager (RPM) found
in devices based on Qualcomm 8974 and newer platforms.

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