[Mellanox] optimize platform API import time (#10815)

- Why I did it
"import sonic_platform" takes about 600ms ~ 1000ms, it is kind of slow. After this optimization, the time is about 100ms. The benefit is that those CLIs which does not need the slow import sentence would be faster than before.

- How I did it
Find slow import and call them when need.

- How to verify it
Measure the import time.

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

@@ -30,7 +30,6 @@ try:
 
     from . import utils
     from .device_data import DeviceDataManager
-    from .sfp import SFP, deinitialize_sdk_handle
 except ImportError as e:
     raise ImportError (str(e) + "- required module not found")
 
@@ -113,6 +112,8 @@ class Chassis(ChassisBase):
         if self.sfp_event:
             self.sfp_event.deinitialize()
 
+        if self._sfp_list:
+            from .sfp import SFP, deinitialize_sdk_handle
             if SFP.shared_sdk_handle:
                 deinitialize_sdk_handle(SFP.shared_sdk_handle)
 

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

@@ -17,7 +17,6 @@
 
 import glob
 import os
-from sonic_py_common import device_info
 
 from . import utils
 
@@ -173,6 +172,7 @@ class DeviceDataManager:
     @classmethod
     @utils.read_only_cache()
     def get_platform_name(cls):
+        from sonic_py_common import device_info
         return device_info.get_platform()
 
     @classmethod