raid1: Relace raise_barrier/lower_barrrier with freeze_array/unfreeze_array for recon...

raid1: Relace raise_barrier/lower_barrrier with freeze_array/unfreeze_array for reconfigure the array.

We used raise_barrier to suspend nornal IO while we reconfigure the
array. Now we replace it with freeze_array.
Raise_barrier only suspends normal IO.  But freeze_array not only susend
nornal io,but it can suspend resync io. For the place where call
raise_barrier for reconfigure, it don't has a problem.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>