perf arm-spe: Update --itrace help text

perf arm-spe: Update --itrace help text

The --itrace help now needs updating to reflect that
the --itrace=b argument sythesises branches as well
as branch misses.

Signed-off-by: Graham Woodward <graham.woodward@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: Leo Yan <leo.yan@arm.com>
Cc: nd@arm.com
Cc: mike.leach@linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20241025143009.25419-5-graham.woodward@arm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>