Introduce clang-format

An automated and opinionated style for code. We can decide to change the
style and have the source updated by the clang-format tool by running:

    make format

I've based the style on the Google style with exceptions to better
match
the current source style.

Change-Id: I43f85c7d4ce02ca999805558b25fcab2e43859c6
diff --git a/inc/cpu.h b/inc/cpu.h
index 43bd356..0dc561b 100644
--- a/inc/cpu.h
+++ b/inc/cpu.h
@@ -50,4 +50,4 @@
 void vcpu_on(struct vcpu *v);
 void vcpu_off(struct vcpu *v);
 
-#endif  /* _CPU_H */
+#endif /* _CPU_H */