arm64/process.c: fix Wmissing-prototypes build warnings

Fix GCC warnings reported when building with "-Wmissing-prototypes":

  arch/arm64/kernel/process.c:261:6: warning: no previous prototype for '__show_regs' [-Wmissing-prototypes]
      261 | void __show_regs(struct pt_regs *regs)
          |      ^~~~~~~~~~~
  arch/arm64/kernel/process.c:307:6: warning: no previous prototype for '__show_regs_alloc_free' [-Wmissing-prototypes]
      307 | void __show_regs_alloc_free(struct pt_regs *regs)
          |      ^~~~~~~~~~~~~~~~~~~~~~
  arch/arm64/kernel/process.c:365:5: warning: no previous prototype for 'arch_dup_task_struct' [-Wmissing-prototypes]
      365 | int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
          |     ^~~~~~~~~~~~~~~~~~~~
  arch/arm64/kernel/process.c:546:41: warning: no previous prototype for '__switch_to' [-Wmissing-prototypes]
      546 | __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
          |                                         ^~~~~~~~~~~
  arch/arm64/kernel/process.c:710:25: warning: no previous prototype for 'arm64_preempt_schedule_irq' [-Wmissing-prototypes]
      710 | asmlinkage void __sched arm64_preempt_schedule_irq(void)
          |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~

Link: https://lore.kernel.org/lkml/202103192250.AennsfXM-lkp@intel.comReported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Link: https://lore.kernel.org/r/1616568899-986-1-git-send-email-maninder1.s@samsung.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/processor.h

@@ -251,6 +251,8 @@ unsigned long get_wchan(struct task_struct *p);
 extern struct task_struct *cpu_switch_to(struct task_struct *prev,
 					 struct task_struct *next);
 
+asmlinkage void arm64_preempt_schedule_irq(void);
+
 #define task_pt_regs(p) \
 	((struct pt_regs *)(THREAD_SIZE + task_stack_page(p)) - 1)
 

arch/arm64/include/asm/thread_info.h

@@ -55,6 +55,8 @@ void arch_setup_new_exec(void);
 #define arch_setup_new_exec     arch_setup_new_exec
 
 void arch_release_task_struct(struct task_struct *tsk);
+int arch_dup_task_struct(struct task_struct *dst,
+				struct task_struct *src);
 
 #endif
 

arch/arm64/kernel/process.c

@@ -57,6 +57,8 @@
 #include <asm/processor.h>
 #include <asm/pointer_auth.h>
 #include <asm/stacktrace.h>
+#include <asm/switch_to.h>
+#include <asm/system_misc.h>
 
 #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
 #include <linux/stackprotector.h>