perf docs: Refine the description for the buffer size

perf docs: Refine the description for the buffer size

Current description for the AUX trace buffer size is misleading. When a
user specifies the option '-m,512M', it represents a size value in bytes
(512MiB) but not 512M pages (512M x 4KiB regard to a page of 4KiB).

Make the document clear that the normal buffer and the AUX tracing
buffer share the same semantics. Syncs the documents for consistent
text.

Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240812093459.2575278-1-leo.yan@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>