perf ftrace: Reuse target::initial_delay

Replace perf_ftrace::initial_delay with target::initial_delay.
Specifying a negative initial_delay is meaningless for ftrace in
practice but allowed here.

Signed-off-by: Changbin Du <changbin.du@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Hui Wang <hw.huiwang@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230302031146.2801588-4-changbin.du@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>