diag: Add support for querying the diag transport

Tools can query the active transport being used by diag using the
transport query command and then configure the qdss trace sink.

Change-Id: I549090a6b3437d5ddc86cddd28baecbd4d1ac5ad
Signed-off-by: Sreelakshmi Gownipalli <sgownipa@codeaurora.org>