perf/core improvements and fixes:

User visible:

- Print callchains asked for events requested via 'perf trace --event' too:
  (Arnaldo Carvalho de Melo)

  # trace -e nanosleep --call dwarf --event sched:sched_switch/call-graph=fp/ usleep 1
   0.346 (0.005 ms): usleep/24428 nanosleep(rqtp: 0x7fffa15a0540) ...
   0.346 (        ): sched:sched_switch:usleep:24428 [120] S ==> swapper/3:0 [120])
                                    __schedule+0xfe200402 ([kernel.kallsyms])
                                    schedule+0xfe200035 ([kernel.kallsyms])
                                    do_nanosleep+0xfe20006f ([kernel.kallsyms])
                                    hrtimer_nanosleep+0xfe2000dc ([kernel.kallsyms])
                                    sys_nanosleep+0xfe20007a ([kernel.kallsyms])
                                    do_syscall_64+0xfe200062 ([kernel.kallsyms])
                                    return_from_SYSCALL_64+0xfe200000 ([kernel.kallsyms])
                                    __nanosleep+0xffff005b8d602010 (/usr/lib64/libc-2.22.so)
   0.400 (0.059 ms): usleep/24428  ... [continued]: nanosleep()) = 0
                                    __nanosleep+0x10 (/usr/lib64/libc-2.22.so)
                                    usleep+0x34 (/usr/lib64/libc-2.22.so)
                                    main+0x1eb (/usr/bin/usleep)
                                    __libc_start_main+0xf0 (/usr/lib64/libc-2.22.so)
                                    _start+0x29 (/usr/bin/usleep)

- Allow requesting that some CPUs or PIDs be highlighted in 'perf sched map' (Jiri Olsa)

- Compact 'perf sched map' to show just CPUs with activity, improving the output
  in high core count systems (Jiri Olsa)

- Fix segfault with 'perf trace --no-syscalls -e syscall-names' by bailing out
  such request, doesn't make sense to ask for no syscalls and then specify which
  ones should be printed (Arnaldo Carvalho de Melo)

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