Add stratum-tofino driver

This patch also introduces a new driver property flag to indicate
whether a P4Runtime target supports default table entries or not.
Stratum targets built against the current version of p4lang/PI do not.

Change-Id: I1fbb57521516bee99057319ed1695cb05b68ee7c
diff --git a/drivers/bmv2/src/main/resources/bmv2-drivers.xml b/drivers/bmv2/src/main/resources/bmv2-drivers.xml
index 9638f9f..0672f73 100644
--- a/drivers/bmv2/src/main/resources/bmv2-drivers.xml
+++ b/drivers/bmv2/src/main/resources/bmv2-drivers.xml
@@ -31,6 +31,9 @@
             hwVersion="BMv2 simple_switch" swVersion="Stratum" extends="stratum">
         <behaviour api="org.onosproject.net.behaviour.PiPipelineProgrammable"
                    impl="org.onosproject.drivers.bmv2.Bmv2PipelineProgrammable"/>
+        <!-- The current version of p4lang/PI used in Stratum does not
+        support reading default table entries -->
+        <property name="supportDefaultTableEntry">false</property>
     </driver>
 </drivers>