spmi: add SPMI PMIC arbiter debug bus driver

Add a new SPMI bus driver which can manage the SPMI debug bus
found on SPMI PMIC arbiter version 5 and above.  This debug
bus has read and write access to all PMIC peripherals regardless
of ownership configurations.  It cannot be used on production
devices because it is disabled by an eFuse.

Change-Id: I7dd7171d775db02269b98bb079bdccf5d0f4aae4
Signed-off-by: David Collins <collinsd@codeaurora.org>