ARM: dts: msm: switch to RPMh controlled PMIC regulators for SDM855

Replace the stub-regulator device nodes for the PM855 and PM855L
regulators with rpmh-regulator device nodes.  This ensures that
consumers are able to modify the physical state of these PMIC
regulators.

Also update the minimum and maximum voltages allowed for each
regulator to match the most recently documented limits.  These
limits are enforced by the AOP.

Change-Id: Ibff6e75b5ca6cc97d6bf091810a927553e8fcf79
Signed-off-by: David Collins <collinsd@codeaurora.org>