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

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

CRs-Fixed: 2094360
Change-Id: I458b5b6e0633cf27836586382e6c5fcbee9b81ef
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>