qbt1000: Validate FP app name before qseecom_start_app

Validate the name of the client app before passing it to
qseecom_start_app.

CRs-Fixed: 2006695
Change-Id: I9c6b16050d4f6fc94827021c7b0f2ab292452f60
Signed-off-by: Abir Ghosh <abirg@codeaurora.org>