tracing: kprobe-event: Allocate string buffers from heap

Allocate temporary string buffers for parsing kprobe-events
from heap instead of stack.

Link: https://lore.kernel.org/all/175323427627.57270.5105357260879695051.stgit@devnote2/



Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>