msm: smd: Reset the PIL string in edge_to_pid table

When configuration data for SMD is available through Device Tree, reset
the default subsystem_name information in edge_to_pid table. This will
enable the clients of SMD to identify unsupported edges.

Change-Id: I394cba40ae99a1bc4c255a7abf5188dbdde18a6f
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>