Add powerHintAsync functionality

Add an async version of powerHint called powerHintAsync.

Bug: 62377008
Test: Take systrace, confirm powerHint is now an async HIDL transaction

Change-Id: I7c4d850ef17c909977675771d6c2b8a3fa1609d2
diff --git a/power/1.1/default/Power.cpp b/power/1.1/default/Power.cpp
index bf7c1fc..b5d0c84 100644
--- a/power/1.1/default/Power.cpp
+++ b/power/1.1/default/Power.cpp
@@ -165,6 +165,11 @@
     return Void();
 }
 
+Return<void> Power::powerHintAsync(PowerHint hint, int32_t data) {
+    // just call the normal power hint in this oneway function
+    return powerHint(hint, data);
+}
+
 } // namespace implementation
 }  // namespace V1_1
 }  // namespace power