perf bench syscall: Introduce bench_syscall_common()

In the current code, there is only a basic syscall benchmark via
getppid, this is not enough. Introduce bench_syscall_common() so that we
can add more syscalls to benchmark.

This is preparation for later patch, no functionality change.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.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/1668052208-14047-3-git-send-email-yangtiezhu@loongson.cn


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>