Fix keylayouts to use BACK instead of incorrect BUTTON_BACK.

Fix duplicate keys in a couple of the onza controllers.  Also, add them to the
Makefile so they actually get included in the build.

Bug: 8292749
Change-Id: I8246155f84d0c3c75b21e37fb579227fda76e197
diff --git a/data/keyboards/Vendor_046d_Product_c219.kl b/data/keyboards/Vendor_046d_Product_c219.kl
index 431dd03..2fa964c 100644
--- a/data/keyboards/Vendor_046d_Product_c219.kl
+++ b/data/keyboards/Vendor_046d_Product_c219.kl
@@ -23,7 +23,7 @@
 key 310 BUTTON_L2
 key 311 BUTTON_R2
 key 313 BUTTON_START
-key 312 BUTTON_BACK
+key 312 BACK
 key 314 BUTTON_THUMBL
 key 315 BUTTON_THUMBR