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/arch.h b/inc/arch.h
index 84624fb..195d149 100644
--- a/inc/arch.h
+++ b/inc/arch.h
@@ -5,4 +5,4 @@
 
 void arch_putchar(char c);
 
-#endif  /* _ARCH_H */
+#endif /* _ARCH_H */