raid1: Add a field array_frozen to indicate whether raid in freeze state.

Because the following patch will rewrite the content between normal IO
and resync IO. So we used a parameter to indicate whether raid is in freeze
array.

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

diff --cc drivers/md/raid1.c
Simple merge

diff --cc drivers/md/raid1.h
Simple merge