ring-buffer/selftest: Add ring-buffer mapping test

Map a ring-buffer, validate the meta-page before and after emitting few
events. Also check ring-buffer mapping boundaries and finally ensure the
tracing snapshot is mutually exclusive.

Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-6-vdonnefort@google.com

Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: linux-kselftest@vger.kernel.org
Acked-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>