groupextcommands: revise 9 bytes postcode object

Store first 8 bytes in primary code, and store the last byte in
secondary code array.

Test results:
```
root@bmc:~# busctl call xyz.openbmc_project.State.Boot.PostCode0 /xyz/openbmc_project/State/Boot/PostCode0 xyz.openbmc_project.State.Boot.PostCode GetPostCodes q 1 -j
{
        "type" : "a(tay)",
        "data" : [
                [
                        [
                                72623859790382856,
                                [
                                        9
                                ]
                        ],
                        [
                                1230066625199609624,
                                [
                                        25
                                ]
                        ],
                        [
                                2387509390608836392,
                                [
                                        41
                                ]
                        ],
                        [
                                2387509390608836392,
                                [
                                        48
                                ]
                        ]
                ]
        ]
}
```

Change-Id: Id58c457f2107b447daed90bd3cd3b2a268e1b28f
Signed-off-by: Potin Lai <potin.lai@quantatw.com>
1 file changed