m68k/mac: Make mac_hid_mouse_emulate_buttons() declaration visible

drivers/char/keyboard.c: In function 'kbd_keycode':
drivers/char/keyboard.c:1142: error: implicit declaration of function 'mac_hid_mouse_emulate_buttons'

The forward declaration of mac_hid_mouse_emulate_buttons() is not visible on
m68k because it's hidden in the middle of a big #ifdef block.

Move it to <linux/kbd_kern.h>, correct the type of the second parameter, and
include <linux/kbd_kern.h> where needed.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>