hikey: powerHAL: Update PowerHAL for top-app category and other tweaks

The initial EAS hikey powerhal was added before N was released, which
introduced the top-app category. So refactor the code to use top-app.

This also tweaks the build so that the module can be more easily
reused on other hardware.

Change-Id: I2847cbf62ea45b15fa2b8d3ee249c153cea351b0
Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/power/Android.mk b/power/Android.mk
index 2c7e15f..187d56e 100644
--- a/power/Android.mk
+++ b/power/Android.mk
@@ -22,6 +22,6 @@
 LOCAL_MODULE_RELATIVE_PATH := hw
 LOCAL_SHARED_LIBRARIES := liblog libcutils
 LOCAL_SRC_FILES := power_hikey.c
-LOCAL_MODULE := power.hikey
+LOCAL_MODULE := power.$(TARGET_BOARD_PLATFORM)
 LOCAL_MODULE_TAGS := optional
 include $(BUILD_SHARED_LIBRARY)