jailhouse: Use spinlock to allow only one CPU to execute memory phase

So far, we do not disable interrupts so care must be taken that the
calling thread does not migrate to another CPU.

diff --git a/jailhouse b/jailhouse
index 7d1df051567a5f945f0e80514c579e46e4b93496..f199740b9e73b94ae59105929cb2bfd8f9ddf43f 160000 (submodule)
--- a/jailhouse
+++ b/jailhouse
@@ -1 +1 @@
-Subproject commit 7d1df051567a5f945f0e80514c579e46e4b93496
+Subproject commit f199740b9e73b94ae59105929cb2bfd8f9ddf43f