diag: Add separate read threads for SMD data channels

Currently, diag uses a single thread for reading the data from
the SMD data channels. Make changes in diag so that there is a
separate thread used in reading each SMD data channel.

Change-Id: Ia14efb7f4feb73d832536f0c16be77cd70352bef
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>