Check out "pkvm" branch for Linux

When a user first clones our repo, they should get the 'pkvm' branch.

Change-Id: I7f7a6bba8cd6683f88a816da874e64a7addbcd1e
diff --git a/default.xml b/default.xml
index c7ed834..b16d58a 100644
--- a/default.xml
+++ b/default.xml
@@ -10,7 +10,7 @@
   <project path="buildroot" name="buildroot" revision="kvmunittests" />
   <project path="kvmtool" name="kvmtool" />
   <project path="kvm-unit-tests" name="kvm-unit-tests" revision="kvmunittests" />
-  <project path="linux" name="linux" />
+  <project path="linux" name="linux" revision="pkvm" />
   <project path="misc" name="misc" />
   <project path="prebuilts" name="prebuilts" clone-depth="1" />