trappy: Add tracing_mark_write as a new event
trappy: Add tracing_mark_write as a new event

Create tracing_mark_write as an event and treat it like such. It overrides data
string processing since it cannot use 'key=value' parsing. Instead it relies on
the tracer to provide one (such as systrace has custom trace format from
userspace events). If tracer cannot provide one, then it just returns a default
dictionary with key 'string' and value as the string in the event.

Signed-off-by: Joel Fernandes <89f39a38232ac523c7644e47b6ca6563177e40b4@google.com>
Reviewed-by: KP Singh <d2841bc036e0f1e3090bf6691da4b34cb2d724be@google.com>

ARM-software/trappy,bjackman/trappy,ARM-software/trappy,bjackman/trappy,ARM-software/trappy,ARM-software/trappy,bjackman/trappy,bjackman/trappy