openrisc: Add prototype for die to bug.h

When compiling with W=1 enabling -Wmissing-prototypes the compiler
warns:

  arch/openrisc/kernel/traps.c:221:17: sing-prototypesrror: no previous prototype for 'die' [-Werror=missing-prototypes]

Fix by adding the prototype to the appropriate header file and including
the header file in the appropriate C files.
Reported-by: Arnd Bergmann <arnd@arndb.de>
Closes: https://lore.kernel.org/linux-kernel/20230810141947.1236730-17-arnd@kernel.org/Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/include/asm/bug.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_OPENRISC_BUG_H
+#define __ASM_OPENRISC_BUG_H
+
+#include <asm-generic/bug.h>
+
+struct pt_regs;
+
+void __noreturn die(const char *str, struct pt_regs *regs, long err);
+
+#endif /* __ASM_OPENRISC_BUG_H */

arch/openrisc/kernel/traps.c

@@ -30,6 +30,7 @@
 #include <linux/kallsyms.h>
 #include <linux/uaccess.h>
 
+#include <asm/bug.h>
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/unwinder.h>

arch/openrisc/mm/fault.c

@@ -18,6 +18,7 @@
 #include <linux/perf_event.h>
 
 #include <linux/uaccess.h>
+#include <asm/bug.h>
 #include <asm/mmu_context.h>
 #include <asm/siginfo.h>
 #include <asm/signal.h>
@@ -30,8 +31,6 @@
  */
 volatile pgd_t *current_pgd[NR_CPUS];
 
-extern void __noreturn die(char *, struct pt_regs *, long);
-
 asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 			      unsigned long vector, int write_acc);