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/y2020/BUILD b/y2020/BUILD
index 32d392a..7c04d99 100644
--- a/y2020/BUILD
+++ b/y2020/BUILD
@@ -77,6 +77,9 @@
         "//frc971:constants",
         "//frc971/control_loops:static_zeroing_single_dof_profiled_subsystem",
         "//frc971/shooter_interpolation:interpolation",
+        "//frc971/zeroing:absolute_and_absolute_encoder",
+        "//frc971/zeroing:absolute_encoder",
+        "//frc971/zeroing:pot_and_absolute_encoder",
         "//y2020/control_loops/drivetrain:polydrivetrain_plants",
         "//y2020/control_loops/superstructure/accelerator:accelerator_plants",
         "//y2020/control_loops/superstructure/control_panel:control_panel_plants",