Display width for `bigint/int` is not compatible with mysql 8.0

## Bug Report
Display width for bigint/int is not compatible with mysql 8.0.We received this defined value using int,so if we define display width as unsigned(>max.int and

### 2. What did you expect to see? (Required)
```
mysql> create table b (a bigint(9223372036854775807));
ERROR 1439 (42000): Display width out of range for column 'a' (max = 4294967295)
mysql> create table a (a bigint(18446744073709551615));
ERROR 1439 (42000): Display width out of range for column 'a' (max = 4294967295)
mysql> create table b (a bigint(18446744073709551616));
ERROR 1439 (42000): Display width out of range for column 'a' (max = 4294967295)

```

### 3. What did you see instead (Required)

```
mysql> create table b (a bigint(9223372036854775807));
ERROR 1439 (42000): Display width out of range for column 'a' (max = 4294967295)
mysql> create table a (a bigint(18446744073709551615));
Query OK, 0 rows affected (0.14 sec)
mysql> create table b (a bigint(18446744073709551616));
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your TiDB version for the right syntax to use line 1 column 45 near "18446744073709551616))"
```
### 4. What is your TiDB version? (Required)

"Release Version"=v7.4.0-alpha
"Git Commit Hash"=05aa17143df86602fef68fced906c6e47a9a00e2