diag: Add support for APQ8084 QPST string

APQ8084 is a new device. Add diag support for sending
appropriate model number for APQ8084 so that QPST
can display the appropriate string.

Change-Id: I51b1b3201d96e2462d75f087d169b5c2a5882d6a
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>