add input vol and current to fixed psu

Signed-off-by: orfar1994 <orfar1994@gmail.com>

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

@@ -190,7 +190,25 @@ def get_temperature_high_threshold(self):
         """
         return None
 
-
+    def get_input_voltage(self):
+        """
+        Retrieves current PSU voltage input
+
+        Returns:
+            A float number, the input voltage in volts, 
+            e.g. 12.1 
+        """
+        return None
+
+    def get_input_current(self):
+        """
+        Retrieves the input current draw of the power supply
+
+        Returns:
+            A float number, the electric current in amperes, e.g 15.4
+        """
+        return None
+
 class Psu(FixedPsu):
     """Platform-specific Psu class"""
     PSU_CURRENT = "power/psu{}_curr"