[Mellanox] Fix issue: SN4600C has 4 CPU core temperature sensors (#9930)

- Why I did it
platform.json of 4600C only has 2 CPU core thermal sensors, but there are 4 actually

- How I did it
Added thermal sensors for CPU core 2 and core 3.

- How to verify it
Build.

device/mellanox/x86_64-mlnx_msn4600c-r0/platform.json

@@ -95,6 +95,12 @@
             {
                 "name": "CPU Core 1 Temp"
             },
+            {
+                "name": "CPU Core 2 Temp"
+            },
+            {
+                "name": "CPU Core 3 Temp"
+            },
             {
                 "name": "CPU Pack Temp"
             }