[Arista] Add components for 720DT-48S (#12217)

Why I did it
Add components data for sonic-mgmt testing

How I did it
Update platform.json and add platform_components.json

How to verify it
Ran sonic-mgmt tests (test_chassis and test_component)

Author: andywongarista

device/arista/x86_64-arista_720dt_48s/platform.json

@@ -1,7 +1,14 @@
 {
     "chassis": {
         "name": "CCS-720DT-48S",
-        "components": [],
+        "components": [
+            {
+               "name": "Aboot()"
+            },
+            {
+               "name": "Scd(addr=0000:00:18.7)"
+            }
+        ],
         "fan_drawers": [
             {
                 "name": "fixed1",

device/arista/x86_64-arista_720dt_48s/platform_components.json

@@ -0,0 +1,10 @@
+{
+    "chassis": {
+        "CCS-720DT-48S": {
+            "component": {
+                "Aboot()": {},
+                "Scd(addr=0000:00:18.7)": {}
+            }
+        }
+    }
+}