ARM: dts: msm: add SPMI PMIC arbiter device for sdm670

Add an SPMI PMIC arbiter device so that it is possible to
communicate with PMICs attached to the SPMI bus.

CRs-Fixed: 2059735
Change-Id: Ib618cd3351f3c4d0b7d5175403a07ba1c7e4e91d
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>