google-ipmi-sys: Add "Entity Id:Entity Instance" mapping to Entity name

Say the system has a JSON file like :
{
    "cpu": [
        {"instance": 1, "name": "CPU0"},
        {"instance": 2, "name": "CPU1"}
    ],
    "memory_module": [
        {"instance": 1, "name": "DIMM_A1"},
        {"instance": 2, "name": "DIMM_A2"},
        {"instance": 3, "name": "DIMM_B1"},
        {"instance": 4, "name": "DIMM_B2"},
        {"instance": 5, "name": "DIMM_C1"},
        {"instance": 6, "name": "DIMM_C2"},
        {"instance": 7, "name": "DIMM_D1"},
        {"instance": 8, "name": "DIMM_D2"},
        {"instance": 9, "name": "DIMM_E1"},
        {"instance": 10, "name": "DIMM_E2"},
        {"instance": 11, "name": "DIMM_F1"},
    ],
    "add_in_card": [
        {"instance": 1, "name": "slot1"},
        {"instance": 2, "name": "slot2"},
        {"instance": 3, "name": "slot3"},
        {"instance": 4, "name": "slot5"}
    ],
    "storage_device": [
        {"instance": 1, "name": "SATA0"},
        {"instance": 2, "name": "SATA1"},
        {"instance": 3, "name": "SATA2"},
        {"instance": 4, "name": "SATA3"}
    ]
}

The system can query the BMC for an Entity name given the Entity ID and Entity Instance.

Tested:
Yes;
1) Sending GetEntityName command; Expecting error since entity ID and
entity instance are not specified.
root@adler:~# ipmitool -I dbus raw 0x2e 0x32 0x79 0x2b 0x00 0x06
Unable to send RAW command (channel=0x0 netfn=0x2e lun=0x0 cmd=0x32
rsp=0xc7): Request data length invalid

2) Sending GetEntityName command; Expecting error since entity instance
is not specified.
root@adler:~# ipmitool -I dbus raw 0x2e 0x32 0x79 0x2b 0x00 0x06 0x01
Unable to send RAW command (channel=0x0 netfn=0x2e lun=0x0 cmd=0x32
rsp=0xc7): Request data length invalid

3) Sending GetEntityName command; Expecting error since Entity Id = 0x07
is not supported.
root@adler:~# ipmitool -I dbus raw 0x2e 0x32 0x79 0x2b 0x00 0x06 0x07 0x01
Unable to send RAW command (channel=0x0 netfn=0x2e lun=0x0 cmd=0x32
rsp=0xcc): Invalid data field in request

4) Sending GetEntityName command; Expecting error since Entity Instance
= 0x06 is not added in the JSON file.
root@adler:~# ipmitool -I dbus raw 0x2e 0x32 0x79 0x2b 0x00 0x06 0x3
0x06
Unable to send RAW command (channel=0x0 netfn=0x2e lun=0x0 cmd=0x32
rsp=0xcc): Invalid data field in request

5) Sending GetEntityName command; Expecting success.
root@adler:~# ipmitool -I dbus raw 0x2e 0x32 0x79 0x2b 0x00 0x06 0x3
0x01
 79 2b 00 06 04 43 50 55 30
root@adler:~# ipmitool -I dbus raw 0x2e 0x32 0x79 0x2b 0x00 0x06 0x0B
0x01
 79 2b 00 06 05 73 6c 6f 74 31
root@adler:~#

Change-Id: Idf6caae863acacd62460cbb7f73bf56fc927bcff
Signed-off-by: Jaghathiswari Rankappagounder Natarajan <jaghu@google.com>
diff --git a/main.hpp b/main.hpp
index f1cfccf..dfe8f29 100644
--- a/main.hpp
+++ b/main.hpp
@@ -19,6 +19,8 @@
     SysPcieSlotCount = 4,
     // The Sys pcie slot to i2c bus mapping command.
     SysPcieSlotI2cBusMapping = 5,
+    // The Sys "entity id:entity instance" to entity name mapping command.
+    SysEntityName = 6,
 };
 
 } // namespace ipmi