sel4: Move sel4 kernel and libs to 3p

We've made changes to these repositories, but they're still 3p code
primarily. Move over to the 3p moniker to reduce automated security
complaints on code we can't directly influence.

Change-Id: Ieecf6940a3fe5bcb2e6d4c7fa9e8cfcf5393bd5a

manifest.xml

diff --git a/manifest.xml b/manifest.xml
index 4af0320..dc7f964 100644
--- a/manifest.xml
+++ b/manifest.xml
@@ -36,8 +36,10 @@
   <!-- BEGIN cantrip components -->
   <project name="sw/cantrip/userland"  path="cantrip/projects/cantrip" />
   <project name="sw/cantrip/minisel"   path="cantrip/projects/minisel" />
-  <project name="sw/cantrip/sel4"      path="cantrip/kernel" />
-  <project name="sw/cantrip/sel4_libs" path="cantrip/projects/seL4_libs" />
+
+  <!-- We have changes in the following two projects -->
+  <project name="3p/sel4/sel4"         path="cantrip/kernel" />
+  <project name="3p/sel4/sel4_libs"    path="cantrip/projects/seL4_libs" />
 
   <project name="3p/sel4/camkes-tool"            path="cantrip/projects/camkes-tool" />
   <project name="3p/sel4/camkes"                 path="cantrip/projects/camkes" />