Don't list dynamic if a slot doesn't support DAP

If a slot doesn't support dynamic partitions, it's impossible to list
dynamic partitions on that slot. And we should just fall back to the
regular A/B in this case.

Bug: 180025432
Test: apply a retrofit package
Change-Id: I16c457b591e8c1d0cf1077a7be50dd9d8f61b8eb
diff --git a/common/dynamic_partition_control_interface.h b/common/dynamic_partition_control_interface.h
index 8368eeb..61127d4 100644
--- a/common/dynamic_partition_control_interface.h
+++ b/common/dynamic_partition_control_interface.h
@@ -134,11 +134,13 @@
   // allocated space for snapshot updates.
   virtual bool ResetUpdate(PrefsInterface* prefs) = 0;
 
-  // Reads the dynamic partitions metadata from the current slot, and puts the
+  // Reads the dynamic partitions metadata from the given slot, and puts the
   // name of the dynamic partitions with the current suffix to |partitions|.
   // Returns true on success.
   virtual bool ListDynamicPartitionsForSlot(
-      uint32_t current_slot, std::vector<std::string>* partitions) = 0;
+      uint32_t slot,
+      uint32_t current_slot,
+      std::vector<std::string>* partitions) = 0;
 
   // Finds a possible location that list all block devices by name; and puts
   // the result in |path|. Returns true on success.