tracing: Limit trace_seq size to just 8K and not depend on architecture PAGE_SIZE

The trace_seq buffer is used to print out entire events. It's typically
set to PAGE_SIZE * 2 as there's some events that can be quite large.

As a side effect, writes to trace_marker is limited by both the size of the
trace_seq buffer as well as the ring buffer's sub-buffer size (which is a
power of PAGE_SIZE). By limiting the trace_seq size, it also limits the
size of the largest string written to trace_marker.

trace_seq does not need to be dependent on PAGE_SIZE like the ring buffer
sub-buffers need to be. Hard code it to 8K which is PAGE_SIZE * 2 on most
architectures. This will also limit the size of trace_marker on those
architectures with greater than 4K PAGE_SIZE.

Link: https://lore.kernel.org/all/20240302111244.3a1674be@gandalf.local.home/
Link: https://lore.kernel.org/linux-trace-kernel/20240304191342.56fb1087@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>