Change primary postcode interface to byte 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(ayay)",
        "data" : [
                [
                        [
                                [
                                        1,
                                        2,
                                        3,
                                        4,
                                        5,
                                        6,
                                        7,
                                        8,
                                        9
                                ],
                                []
                        ],
                        [
                                [
                                        17,
                                        18,
                                        19,
                                        20,
                                        21,
                                        22,
                                        23,
                                        24,
                                        25
                                ],
                                []
                        ],
                        [
                                [
                                        33,
                                        34,
                                        35,
                                        36,
                                        37,
                                        38,
                                        39,
                                        40,
                                        41
                                ],
                                []
                        ]
                ]
        ]
}
```

Change-Id: I81387df590c2c6781451c6dbcc030d48ca011eb6
Signed-off-by: Potin Lai <potin.lai@quantatw.com>
diff --git a/inc/post_code.hpp b/inc/post_code.hpp
index 26b5c48..db7533f 100644
--- a/inc/post_code.hpp
+++ b/inc/post_code.hpp
@@ -50,7 +50,7 @@
     }
 };
 using EventPtr = std::unique_ptr<sd_event, EventDeleter>;
-using primarycode_t = uint64_t;
+using primarycode_t = std::vector<uint8_t>;
 using secondarycode_t = std::vector<uint8_t>;
 using postcode_t = std::tuple<primarycode_t, secondarycode_t>;
 namespace fs = std::filesystem;