arch: consolidate arch_irq_work_raise prototypes

The prototype was hidden in an #ifdef on x86, which causes a warning:

kernel/irq_work.c:72:13: error: no previous prototype for 'arch_irq_work_raise' [-Werror=missing-prototypes]

Some architectures have a working prototype, while others don't.
Fix this by providing it in only one place that is always visible.

Reviewed-by: Alexander Gordeev <[e-mail]>
Acked-by: Catalin Marinas <[e-mail]>
Acked-by: Palmer Dabbelt <[e-mail]>
Acked-by: Guo Ren <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

arch/arm/include/asm/irq_work.h

···
 	return is_smp();
 }
 
-extern void arch_irq_work_raise(void);
-
 #endif /* _ASM_ARM_IRQ_WORK_H */

arch/arm64/include/asm/irq_work.h

···
 #ifndef __ASM_IRQ_WORK_H
 #define __ASM_IRQ_WORK_H
 
-extern void arch_irq_work_raise(void);
-
 static inline bool arch_irq_work_has_interrupt(void)
 {
 	return true;

arch/csky/include/asm/irq_work.h

···
 {
 	return true;
 }
-extern void arch_irq_work_raise(void);
+
 #endif /* __ASM_CSKY_IRQ_WORK_H */

arch/powerpc/include/asm/irq_work.h

···
 {
 	return true;
 }
-extern void arch_irq_work_raise(void);
 
 #endif /* _ASM_POWERPC_IRQ_WORK_H */

arch/riscv/include/asm/irq_work.h

···
 {
 	return IS_ENABLED(CONFIG_SMP);
 }
-extern void arch_irq_work_raise(void);
+
 #endif /* _ASM_RISCV_IRQ_WORK_H */

arch/s390/include/asm/irq_work.h

···
 	return true;
 }
 
-void arch_irq_work_raise(void);
-
 #endif /* _ASM_S390_IRQ_WORK_H */

arch/x86/include/asm/irq_work.h

···
 {
 	return boot_cpu_has(X86_FEATURE_APIC);
 }
-extern void arch_irq_work_raise(void);
 #else
 static inline bool arch_irq_work_has_interrupt(void)
 {

include/linux/irq_work.h

···
 void irq_work_run(void);
 bool irq_work_needs_cpu(void);
 void irq_work_single(void *arg);
+
+void arch_irq_work_raise(void);
+
 #else
 static inline bool irq_work_needs_cpu(void) { return false; }
 static inline void irq_work_run(void) { }