ARM: dts: msm: Add regulator device constraints and labels for msmsamarium

Utilize the QPNP regulator devices on msmsamarium targets.  Add
voltage constraints and supply chain mapping via a new target
specific device tree include file.

Also add a stub-regulator device to support voltage corner
requests for VDD_CX (PMA8084 S2).

Change-Id: I329d12cc92fe12fa74f928fb2b0dbef35281bb00
Signed-off-by: David Collins <collinsd@codeaurora.org>