coresight: have trace_printk only log the actual data to STM

The trace_printk, when configured to process printk strings before
storing them in the internal ring buffer, currently also logs the
complete internal buffer data structure to the STM. Instead it
should only log the string output obtained after processing the
printk format and arguments. Changing the stm_log call to only
log this relevant data.

Change-Id: Ia33109f95fb84fa1606247a861deeaedd2f95d3f
Signed-off-by: Pushkar Joshi <pushkarj@codeaurora.org>