msm: rpm-regulator-smd: Add support for LDO bypass mode disable

Add support in the rpm-regulator-smd driver for the "bypa"
bypass mode disallow parameter.  This parameter can be used to
instruct the RPM that a given LDO should never be put into
bypass mode because its load is sensitive to voltage supply
noise.

Change-Id: I34fdcdb88107f94b78f2ace4a0512fe4ca94779c
Signed-off-by: David Collins <collinsd@codeaurora.org>