msm: msm_bus: Add basic device tree parsing for ad-hoc topology

Add basic device tree usage for ad-hoc bus topologies.

Change-Id: I733732f3b1d8b89fef0e75716967b4e34632df65
Signed-off-by: Dan Sneddon <dsneddon@codeaurora.org>
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>