m68k: kernel: Add and use "traps.h"

When building with W=1:

    arch/m68k/kernel/traps.c:754:17: warning: no previous prototype for ‘buserr_c’ [-Wmissing-prototypes]
      754 | asmlinkage void buserr_c(struct frame *fp)
	  |                 ^~~~~~~~
    arch/m68k/kernel/traps.c:1140:17: warning: no previous prototype for ‘set_esp0’ [-Wmissing-prototypes]
     1140 | asmlinkage void set_esp0(unsigned long ssp)
	  |                 ^~~~~~~~
    arch/m68k/kernel/traps.c:1155:17: warning: no previous prototype for ‘fpemu_signal’ [-Wmissing-prototypes]
     1155 | asmlinkage void fpemu_signal(int signal, int code, void *addr)
	  |                 ^~~~~~~~~~~~
    arch/m68k/kernel/traps.c:1149:17: warning: no previous prototype for ‘fpsp040_die’ [-Wmissing-prototypes]
     1149 | asmlinkage void fpsp040_die(void)
	  |                 ^~~~~~~~~~~

Fix this by introducing a new header file "traps.h" for holding the
prototypes of functions implemented in arch/m68k/kernel/traps.c.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/652cbbb1c9e339980a86068ebdd0a69362324af8.1694613528.git.geert@linux-m68k.org

arch/m68k/kernel/traps.c

@@ -41,6 +41,8 @@
 #include <asm/siginfo.h>
 #include <asm/tlbflush.h>
 
+#include "traps.h"
+
 static const char *vec_names[] = {
 	[VEC_RESETSP]	= "RESET SP",
 	[VEC_RESETPC]	= "RESET PC",

arch/m68k/kernel/traps.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+
+struct frame;
+
+asmlinkage void buserr_c(struct frame *fp);
+asmlinkage void fpemu_signal(int signal, int code, void *addr);
+asmlinkage void fpsp040_die(void);
+asmlinkage void set_esp0(unsigned long ssp);