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

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

When building with W=1:

    arch/m68k/kernel/ptrace.c:275:16: warning: no previous prototype for ‘syscall_trace_enter’ [-Wmissing-prototypes]
      275 | asmlinkage int syscall_trace_enter(void)
	  |                ^~~~~~~~~~~~~~~~~~~
    arch/m68k/kernel/ptrace.c:288:17: warning: no previous prototype for ‘syscall_trace_leave’ [-Wmissing-prototypes]
      288 | asmlinkage void syscall_trace_leave(void)
	  |                 ^~~~~~~~~~~~~~~~~~~

Fix this by introducing a new header file "ptrace.h" for holding the
prototypes of functions implemented in arch/m68k/kernel/ptrace.c.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/b4b3577b2149ebd65c3b3c7acccebc0e7e596f9d.1694613528.git.geert@linux-m68k.org