MultiHal 2.0 - setOperationMode and init direct channel flags

Implement setOperationMode method of HalProxy object and initialized the
direct channel flag for the sensors list. Also create some unit tests to
test both of these new additions in HalProxy_test.cpp.

Bug: 136511617
Test: Tested using unit tests and tested on device with both fake
      subhals

Change-Id: I4e39ca0e94b3e109706d628612d1db9c98aca053
diff --git a/sensors/2.0/multihal/Android.bp b/sensors/2.0/multihal/Android.bp
index 44dddfd..697bf9e 100644
--- a/sensors/2.0/multihal/Android.bp
+++ b/sensors/2.0/multihal/Android.bp
@@ -45,6 +45,7 @@
     ],
     init_rc: ["android.hardware.sensors@2.0-service-multihal.rc"],
     vintf_fragments: ["android.hardware.sensors@2.0-multihal.xml"],
+    cflags: ["-DLOG_TAG=\"SensorsMultiHal\""],
 }
 
 cc_library_headers {