ringbuffer/selftest: Add basic selftest to test changing subbuf order

ringbuffer/selftest: Add basic selftest to test changing subbuf order

Add a self test that will write into the trace buffer with differ trace
sub buffer order sizes.

Link: https://lore.kernel.org/linux-trace-kernel/20231219185631.520496304@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>