Bluetooth: GOEP: Improve TLV triplet encoding and parsing

Add a structure `struct bt_obex_tlv` to pass/save the one TLV info.

Use a array of `struct bt_obex_tlv` as the set of all TLV-triplets.
Update the following functions to  support the feature, including
`bt_obex_add_header_app_param`, `bt_obex_add_header_auth_challenge`,
and `bt_obex_add_header_auth_rsp`.

Add a function `bt_obex_tlv_parse` to parse the encoded TLV-triplets.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>