drivers: md: Unify common definitions of raid1 and raid10

These definitions are being moved to raid1-10.c.

Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>