Pull the medium-specific pieces out of the common code

Change-Id: I9cd1824a6bf535e285553fbe5f79f6d72919f048
diff --git a/motors/BUILD b/motors/BUILD
index e75f74b..fd53dd0 100644
--- a/motors/BUILD
+++ b/motors/BUILD
@@ -20,6 +20,7 @@
 
 cc_library(
   name = 'motor',
+  visibility = ['//visibility:public'],
   hdrs = [
     'motor.h',
   ],
@@ -34,7 +35,7 @@
 
     '//motors/peripheral:adc',
     '//motors/peripheral:can',
-    '//motors/usb:legacy',
+    '//motors/usb:cdc',
   ],
   restricted_to = mcu_cpus,
 )
@@ -96,6 +97,7 @@
 
 cc_library(
   name = 'math',
+  visibility = ['//visibility:public'],
   hdrs = [
     'math.h',
   ],