Revert "xen/events: remove unnecessary call to bind_evtchn_to_cpu()"

Revert "xen/events: remove unnecessary call to bind_evtchn_to_cpu()"

This reverts commit 4201cdbd6cde19a69b862984ef674ce667d526e1.

Customer runing vcpu hot plug/remove in a loop could trigger softlockup.
Backtrace is similar in every test, one of the trace is as below:

 NMI watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [modprobe:3686]
 CPU: 1 PID: 3686 Comm: modprobe Not tainted 4.1.12-94.1.8.el6uek.x86_64 #2
 task: ffff88016be32a00 ti: ffff8800066b0000 task.ti: ffff8800066b0000
 RIP: e030:[<ffffffff81108230>]  [<ffffffff81108230>] smp_call_function_many+0x210/0x260
 Call Trace:
  [<ffffffff8106ef20>] ? __cpa_flush_all+0x50/0x50
  [<ffffffffa02b9000>] ? 0xffffffffa02b9000
  [<ffffffff81108482>] smp_call_function+0x22/0x30
  [<ffffffff811084eb>] on_each_cpu+0x2b/0x70
  [<ffffffffa02b9fff>] ? 0xffffffffa02b9fff
  [<ffffffffa02b9000>] ? 0xffffffffa02b9000
  [<ffffffff810710cc>] change_page_attr_set_clr+0x3fc/0x530
  [<ffffffff8133d011>] ? list_del+0x11/0x40
  [<ffffffff8134b4f9>] ? ddebug_table_free+0x29/0x30
  [<ffffffff81071313>] set_memory_x+0x43/0x50
  [<ffffffff810e6e40>] ? wait_rcu_gp+0x60/0x60
  [<ffffffff811090c8>] set_page_attributes+0x28/0x30
  [<ffffffff81109168>] unset_module_init_ro_nx+0x38/0x70
  [<ffffffff8110c7ce>] free_module+0xae/0x150
  [<ffffffff8110ca1f>] do_init_module+0x1af/0x200
  [<ffffffff8110f361>] load_module+0x5b1/0x740
  [<ffffffff8110c200>] ? mod_sysfs_teardown+0x150/0x150
  [<ffffffff811cd6c2>] ? __vmalloc+0x22/0x30
  [<ffffffff8110baf0>] ? module_sect_show+0x30/0x30
  [<ffffffff8110f674>] SyS_init_module+0x94/0xc0
  [<ffffffff816e4dae>] system_call_fastpath+0x12/0x71

Not clear the root cause lying behind yet, revert above commit help.

Oracle-Bug: 25997062

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>