Grab per-camera constants on the Teensy

Doesn't actually do anything useful with them yet though. Also needs the
mapping filled out.

Change-Id: Ia32d782865a293db7266dfc2d7d8b217fd7b0823
diff --git a/y2019/vision/BUILD b/y2019/vision/BUILD
index 0221254..2bdfd9c 100644
--- a/y2019/vision/BUILD
+++ b/y2019/vision/BUILD
@@ -1,6 +1,7 @@
 load("//aos/build:queues.bzl", "queue_library")
 load("//tools/build_rules:gtk_dependent.bzl", "gtk_dependent_cc_binary", "gtk_dependent_cc_library")
 load("@com_google_protobuf//:protobuf.bzl", "cc_proto_library")
+load("//tools:environments.bzl", "mcu_cpus")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -13,6 +14,8 @@
     name = "constants",
     srcs = ["constants.cc"],
     hdrs = ["constants.h"],
+    compatible_with = mcu_cpus,
+    visibility = ["//visibility:public"],
 )
 
 cc_library(