m68k: q40: Add and use "q40.h"

When building with W=1:

    arch/m68k/q40/q40ints.c:84:13: warning: no previous prototype for ‘q40_init_IRQ’ [-Wmissing-prototypes]
       84 | void __init q40_init_IRQ(void)
	  |             ^~~~~~~~~~~~
    arch/m68k/q40/q40ints.c:112:6: warning: no previous prototype for ‘q40_mksound’ [-Wmissing-prototypes]
      112 | void q40_mksound(unsigned int hz, unsigned int ticks)
	  |      ^~~~~~~~~~~
    arch/m68k/q40/q40ints.c:152:6: warning: no previous prototype for ‘q40_sched_init’ [-Wmissing-prototypes]
      152 | void q40_sched_init (void)
	  |      ^~~~~~~~~~~~~~

Fix this by introducing a new header file "q40.h" for holding the
prototypes of functions implemented in arch/m68k/q40/.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/7f983ce079b176e1e1ac2a7d0c35b36197c5fa6b.1694613528.git.geert@linux-m68k.org

arch/m68k/q40/config.c

@@ -36,16 +36,14 @@
 #include <asm/q40_master.h>
 #include <asm/config.h>
 
-extern void q40_init_IRQ(void);
+#include "q40.h"
+
 static void q40_get_model(char *model);
-extern void q40_sched_init(void);
 
 static int q40_hwclk(int, struct rtc_time *);
 static int q40_get_rtc_pll(struct rtc_pll_info *pll);
 static int q40_set_rtc_pll(struct rtc_pll_info *pll);
 
-extern void q40_mksound(unsigned int /*freq*/, unsigned int /*ticks*/);
-
 static void q40_mem_console_write(struct console *co, const char *b,
 				  unsigned int count);
 

arch/m68k/q40/q40.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/* q40ints.c */
+void q40_init_IRQ(void);
+void q40_mksound(unsigned int hz, unsigned int ticks);
+void q40_sched_init(void);

arch/m68k/q40/q40ints.c

@@ -24,6 +24,8 @@
 #include <asm/q40_master.h>
 #include <asm/q40ints.h>
 
+#include "q40.h"
+
 /*
  * Q40 IRQs are defined as follows:
  *            3,4,5,6,7,10,11,14,15 : ISA dev IRQs