Do not require atomic writes to be power of 2 sized and aligned on length boundary

It contradicts NVMe specification where alignment is only required when atomic
write boundary (NABSPF/NABO) is set and highly limits usage of NVMe atomic writes

Signed-off-by: Vitaliy Filippov <vitalifster@gmail.com>

Author: Vitaliy Filippov

fs/read_write.c

@@ -1802,17 +1802,9 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
 
 int generic_atomic_write_valid(struct kiocb *iocb, struct iov_iter *iter)
 {
-	size_t len = iov_iter_count(iter);
-
 	if (!iter_is_ubuf(iter))
 		return -EINVAL;
 
-	if (!is_power_of_2(len))
-		return -EINVAL;
-
-	if (!IS_ALIGNED(iocb->ki_pos, len))
-		return -EINVAL;
-
 	if (!(iocb->ki_flags & IOCB_DIRECT))
 		return -EOPNOTSUPP;