tracing: full reset during init

I am using the tracing module using the RAM backend on a system with
limited RAM & a buffer that can only store 300ms of tracing data. Current
tracing module starts recording during boot-up & we run out of memory prior
to executing code we actually want to trace.

By reseting buffer metadata here, I can call init() at an arbitrary point
of program execution & the tracing module will reset & start tracing.

I tested on E2E on an ARM M-class MCU by calling init & then reading
buffered tracing data via GDB

Signed-off-by: Galen Krulce <gkrulce@meta.com>