[Mellanox] Initialize PSU API on both host and docker side (#7075)

- Why I did it
There was a change to replace platform utils with sonic platform API in psuutil. However, psu API is not initialized on host side. The PR is to fix it.
Backport of #7016 to the 202012 branch.

- How I did it
Initialize PSU API on both host and non-host side

- How to verify it
Manual test

platform/mellanox/mlnx-platform-api/sonic_platform/platform.py

@@ -16,16 +16,14 @@ except ImportError as e:
 class Platform(PlatformBase):
     def __init__(self):
         PlatformBase.__init__(self)
-        if self._is_host():
-            self._chassis = Chassis()
-            self._chassis.initialize_components()
-            self._chassis.initizalize_system_led()
-            self._chassis.initialize_eeprom()
-        else:
         self._chassis = Chassis()
         self._chassis.initialize_psu()
-            self._chassis.initialize_fan()
         self._chassis.initialize_eeprom()
+        if self._is_host():  
+            self._chassis.initialize_components()
+            self._chassis.initizalize_system_led()  
+        else:    
+            self._chassis.initialize_fan()
             self._chassis.initialize_thermals()
 
     def _is_host(self):