coresight-ost: Add TGID information for FTRACE events

Add TGID information in the header field of OST packets.
TGID is to be used for post processing to obtain an
accurate picture of the system.

Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>
Change-Id: Ic7ac22146911689c0e2d16df6d859da8d45e31c8