Add dummy get/set_lpmode API for SFF8472

The get/set_lpmode API is not applicable to SFF8472 but it should be included
anyway to avoid AttributeErrors from SfpOptoeBase.get/set_lpmode.

sonic_platform_base/sonic_xcvr/api/public/sff8472.py

@@ -37,7 +37,7 @@ def get_transceiver_info(self):
             if len > 0:
                 cable_len = len
                 cable_type = type
- 
+
         xcvr_info = {
             "type": serial_id[consts.ID_FIELD],
             "type_abbrv_name": serial_id[consts.ID_ABBRV_FIELD],
@@ -296,5 +296,26 @@ def get_lpmode_support(self):
     def get_power_override_support(self):
         return False
 
+    def get_lpmode(self):
+        '''
+        Retrieves low power mode status
+
+        Returns:
+            bool: True if module in low power else returns False.
+        '''
+        return False
+
+    def set_lpmode(self, lpmode):
+        '''
+        This function sets LPMode for the module.
+
+        Args:
+            lpmode (bool): False means LPMode Off, True means LPMode On
+
+        Returns:
+            bool: True if the provision succeeds, False if it fails
+        '''
+        return False
+
     def is_copper(self):
         return self.xcvr_eeprom.read(consts.SFP_CABLE_TECH_FIELD) == 'Passive Cable'