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.h b/power/1.1/default/Power.h
index ea9e8c3..e779d64 100644
--- a/power/1.1/default/Power.h
+++ b/power/1.1/default/Power.h
@@ -46,6 +46,7 @@
 
     // Methods from ::android::hardware::power::V1_1::IPower follow.
     Return<void> getSubsystemLowPowerStats(getSubsystemLowPowerStats_cb _hidl_cb) override;
+    Return<void> powerHintAsync(PowerHint hint, int32_t data) override;
 
     // Methods from ::android::hidl::base::V1_0::IBase follow.