fix(m515_curtain_motor): invert position, and use for feedback

User confirmation that position_blinds works well for this device,
so follow that with the extra config options.

Discussion #3730

custom_components/tuya_local/devices/m515_curtain_motor.yaml

@@ -22,6 +22,16 @@ entities:
         range:
           min: 0
           max: 100
+        mapping:
+          - invert: true
+      - id: 2
+        name: current_position
+        type: integer
+        range:
+          min: 0
+          max: 100
+        mapping:
+          - invert: true
       - id: 7
         name: work_state
         type: string