Split up zeroing library BUILD rules

There was no good reason for one build rule to have both the interface
and a bunch of implementations; split it up and make the relevant users
depend on the libraries directly.

Change-Id: If6a0aa49dd7ea588b7325604658bc0594db4aac0
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/frc971/control_loops/BUILD b/frc971/control_loops/BUILD
index 3cdb6ab..31b245b 100644
--- a/frc971/control_loops/BUILD
+++ b/frc971/control_loops/BUILD
@@ -416,6 +416,7 @@
         "//aos/util:trapezoid_profile",
         "//frc971/control_loops:control_loop",
         "//frc971/zeroing",
+        "//frc971/zeroing:pot_and_index",
     ],
 )
 
@@ -661,6 +662,9 @@
         ":static_zeroing_single_dof_profiled_subsystem_test_subsystem_output_fbs",
         "//aos/testing:googletest",
         "//frc971/control_loops:control_loop_test",
+        "//frc971/zeroing:absolute_and_absolute_encoder",
+        "//frc971/zeroing:absolute_encoder",
+        "//frc971/zeroing:pot_and_absolute_encoder",
     ],
 )