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/mm.h b/inc/mm.h
index 1af7496..82066cd 100644
--- a/inc/mm.h
+++ b/inc/mm.h
@@ -40,4 +40,4 @@
 bool mm_ptable_unmap(struct mm_ptable *t, vaddr_t begin, vaddr_t end, int mode);
 void mm_ptable_defrag(struct mm_ptable *t);
 
-#endif  /* _MM_H */
+#endif /* _MM_H */