ARM: dts: msm: switch to RPMh controlled PMIC regulators for sdm670

Replace the stub-regulator device nodes for the PM660 and PM660L
regulators with rpmh-regulator device nodes.  This ensures that
consumers are able to modify the physical state of these PMIC
regulators.

CRs-Fixed: 2084000
Change-Id: I1cd97dd044b57e951c29a19ae68568c920919c08
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>