tracing: Add trace_array_init_printk() to initialize instance trace_printk() buffers

As trace_array_printk() used with not global instances will not add noise to
the main buffer, they are OK to have in the kernel (unlike trace_printk()).
This require the subsystem to create their own tracing instance, and the
trace_array_printk() only writes into those instances.

Add trace_array_init_printk() to initialize the trace_printk() buffers
without printing out the WARNING message.

Reported-by: Sean Paul <sean@poorly.run>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>