diag: Add status functionality to Diag over STM command

The Diag over STM command has been enhanced to include a
status capability. Add this functionality to Diag over
STM processing.

Also, the command code for Diag over STM has changed. Make
modifications to support the newly assigned command code.

Change-Id: I4314ea38b9feb5055a75a692b1b49dbd03a3211d
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>