Moved DrivetrainWriter from y2012

Change-Id: Ife613066312f950d2c11efd1a8db98ff02beb3ec
diff --git a/y2012/BUILD b/y2012/BUILD
index 159632b..2841ee4 100644
--- a/y2012/BUILD
+++ b/y2012/BUILD
@@ -51,6 +51,7 @@
         "//frc971/wpilib:buffered_pcm",
         "//frc971/wpilib:dma",
         "//frc971/wpilib:dma_edge_counting",
+        "//frc971/wpilib:drivetrain_writer",
         "//frc971/wpilib:encoder_and_potentiometer",
         "//frc971/wpilib:gyro_sender",
         "//frc971/wpilib:interrupt_edge_counting",