Pull P4Runtime proto files from p4lang/p4runtime

The protobuf files, along with the specification Madoko source files,
have been moved to p4lang/p4runtime. As a result, we are adding
p4lang/p4runtime as a submodule for this repository.

.gitmodules

@@ -11,3 +11,6 @@
 [submodule "proto/openconfig/public"]
 	path = proto/openconfig/public
 	url = https://github.com/openconfig/public.git
+[submodule "proto/p4runtime"]
+	path = proto/p4runtime
+	url = https://github.com/p4lang/p4runtime.git

proto/configure.ac

@@ -85,7 +85,11 @@ dnl cannot use the path below, which would break 'make dist'
 dnl googleapis_check_f=$ac_abs_confdir/googleapis/google/rpc/status.proto
 googleapis_check_f=$ac_abs_confdir/google/rpc/status.proto
 AC_CHECK_FILE([$googleapis_check_f], [],
-              [AC_MSG_ERROR([Did you run 'git submodule update --init'?])])
+              [AC_MSG_ERROR([Cannot find googleapis; did you run 'git submodule update --init'?])])
+
+p4runtime_check_f=$ac_abs_confdir/p4/v1/p4runtime.proto
+AC_CHECK_FILE([$p4runtime_check_f], [],
+              [AC_MSG_ERROR([Cannot find p4runtime; did you run 'git submodule update --init'?])])
 
 # check for pthreads
 AX_PTHREAD([], [AC_MSG_ERROR([Missing pthread library])])

proto/docs/README.md

@@ -0,0 +1,2 @@
+***The documentation in this directory is deprecated. Please refer to the
+   P4Runtime specification on [p4.org](https://p4.org/specs/).***

proto/p4/config

@@ -0,0 +1 @@
+../p4runtime/proto/p4/config