perf annotate-data: Handle direct use of stack pointer without fbreg

Sometimes compiler generates code to use the stack pointer register
without frame pointer.  As we know RSP is the stack register on x86,
let's treat it as same as fbreg.  But the offset would be opposite
direction so update the debug message accordingly.

Reported-by: Blake Jones <blakejones@google.com>
Link: https://lore.kernel.org/r/20250126210242.1181225-1-namhyung@kernel.org


Signed-off-by: Namhyung Kim <namhyung@kernel.org>