Multihal 2.0 - Implement SubHal discovery

Collect the SubHal pointers discovered from dynamic libs contained
within the multi hal config file.

Bug: 136511617
Test: Compiled with mma -j and observed loading of modules

Change-Id: I148265722e70d4cd56671af9c6f1ff6dde355ae4
diff --git a/sensors/2.0/multihal/HalProxy.h b/sensors/2.0/multihal/HalProxy.h
index b9855a6..e5799fd 100644
--- a/sensors/2.0/multihal/HalProxy.h
+++ b/sensors/2.0/multihal/HalProxy.h
@@ -111,6 +111,11 @@
      * Callback to the sensors framework to inform it that new sensors have been added or removed.
      */
     sp<ISensorsCallback> mDynamicSensorsCallback;
+
+    /**
+     * SubHal object pointers that have been saved from vendor dynamic libraries.
+     */
+    std::vector<ISensorsSubHal*> mSubHalList;
 };
 
 }  // namespace implementation