Add ADC report

Enable building of ADC topic

msg/adc_report.msg

@@ -0,0 +1,3 @@
+uint64 timestamp		# Timestamp in microseconds since boot
+int16[8] channel_id		# ADC channel IDs, negative for non-existent
+float32[8] channel_value	# ADC channel value in volt, valid if channel ID is positive

src/modules/uORB/objects_common.cpp

@@ -297,3 +297,6 @@ ORB_DEFINE(transponder_report, struct transponder_report_s);
 
 #include "topics/gps_inject_data.h"
 ORB_DEFINE(gps_inject_data, struct gps_inject_data_s);
+
+#include "topics/adc_report.h"
+ORB_DEFINE(adc_report, struct adc_report_s);