common: Move hang() to the same header as panic()

At present panic() is in the vsprintf.h header file. That does not seem
like an obvious choice for hang(), even though it relates to panic(). So
let's put hang() in its own header.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Migrate a few more files]
Signed-off-by: Tom Rini <trini@konsulko.com>

arch/arm/lib/div0.c

@@ -4,10 +4,10 @@
  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
  */
 
+#include <hang.h>
+
 /* Replacement (=dummy) for GNU/Linux division-by zero handler */
 void __div0 (void)
 {
-	extern void hang (void);
-
 	hang();
 }