perf/x86: Unify format of events sysfs show

Sysfs show formats of files in /sys/devices/cpu/events/ are not unified,
some end with "\n", and some do not. Modify sysfs show format of events
defined by EVENT_ATTR_STR to end with "\n".

Before:
  $ ls /sys/devices/cpu/events/* | xargs -i sh -c 'echo -n "{}: "; cat -A {}; echo'
  branch-instructions: event=0xc4$

  branch-misses: event=0xc5$

  bus-cycles: event=0x3c,umask=0x01$

  cache-misses: event=0x2e,umask=0x41$

  cache-references: event=0x2e,umask=0x4f$

  cpu-cycles: event=0x3c$

  instructions: event=0xc0$

  ref-cycles: event=0x00,umask=0x03$

  slots: event=0x00,umask=0x4
  topdown-bad-spec: event=0x00,umask=0x81
  topdown-be-bound: event=0x00,umask=0x83
  topdown-fe-bound: event=0x00,umask=0x82
  topdown-retiring: event=0x00,umask=0x80

After:
  $ ls /sys/devices/cpu/events/* | xargs -i sh -c 'echo -n "{}: "; cat -A {}; echo'
  /sys/devices/cpu/events/branch-instructions: event=0xc4$

  /sys/devices/cpu/events/branch-misses: event=0xc5$

  /sys/devices/cpu/events/bus-cycles: event=0x3c,umask=0x01$

  /sys/devices/cpu/events/cache-misses: event=0x2e,umask=0x41$

  /sys/devices/cpu/events/cache-references: event=0x2e,umask=0x4f$

  /sys/devices/cpu/events/cpu-cycles: event=0x3c$

  /sys/devices/cpu/events/instructions: event=0xc0$

  /sys/devices/cpu/events/ref-cycles: event=0x00,umask=0x03$

  /sys/devices/cpu/events/slots: event=0x00,umask=0x4$

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220324031957.135595-1-yangjihong1@huawei.com