ARM: dts: msm: add SPMI debug bus for sdm845

Add an SPMI debug bus device and associated child devices so that
consumers can have unrestricted access to the PMICs on
pre-production devices.  This helps to make debugging easier.

Change-Id: Iecb8818a4c36150e95249b58a380934da43cc1de
Signed-off-by: David Collins <collinsd@codeaurora.org>