diag: Add support for APQ8026 QPST string

APQ8026 is a new device. Add diag support for sending
appropriate model number for APQ8026 so that QPST
can display the appropriate string.

Change-Id: I337693fba4222d2605aa4d489d7c24bebcbd07bf
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>