First stab at BNG support in fabric.p4

This implementation is derived from Deutsche Telekom contribution:
https://github.com/opencord/p4se

It supports basic upstream and downstream termination based on double
VLAN tags and PPPoE, including counters and downstream metering.

Change-Id: I940959f2338d7319654cf665f6cfe2de7200616b
diff --git a/pipelines/fabric/src/main/resources/p4c-out/fabric-bng/bmv2/default/cpu_port.txt b/pipelines/fabric/src/main/resources/p4c-out/fabric-bng/bmv2/default/cpu_port.txt
new file mode 100644
index 0000000..ace9d03
--- /dev/null
+++ b/pipelines/fabric/src/main/resources/p4c-out/fabric-bng/bmv2/default/cpu_port.txt
@@ -0,0 +1 @@
+255