ARM: dts: msms: Adding node for diag bridge interface in sa6155

Adding device tree node to select the diag
bridge interface as USB. This is to configure
diag bridge interface during run time to
resolve bridging issue in case both hsic and
mhi is enabled.

Change-Id: Ic8438540328bf9cc27235ef88b31bdc399cf3df3
Signed-off-by: Arun Prakash <app@codeaurora.org>