tracing: have trace_printk process arguments before storing

trace_printk records its arguments in the internal ring buffer for
them to be processed later. The mapping between the format string
for the particular instance of a trace_printk call and the
arguments is maintained using the instruction pointer internally
in the kernel. However, this makes it harder for an external tool
to process this data, which is necessary when the same data
is logged to the STM and needs to be processed externally.

Change-Id: Ifa2ae5fe1f1fd62c85fac432a581737450781f88
Signed-off-by: Pushkar Joshi <pushkarj@codeaurora.org>