xen: xen_debug_interrupt prototype to global header

The xen_debug_interrupt() function is only called on x86, which has a
prototype in an architecture specific header, but the definition also
exists on others, where the lack of a prototype causes a W=1 warning:

drivers/xen/events/events_2l.c:264:13: error: no previous prototype for 'xen_debug_interrupt' [-Werror=missing-prototypes]

Move the prototype into a global header instead to avoid this warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/20230517124525.929201-1-arnd@kernel.orgSigned-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/xen-ops.h

@@ -72,8 +72,6 @@ void xen_restore_time_memory_area(void);
 void xen_init_time_ops(void);
 void xen_hvm_init_time_ops(void);
 
-irqreturn_t xen_debug_interrupt(int irq, void *dev_id);
-
 bool xen_vcpu_stolen(int vcpu);
 
 void xen_vcpu_setup(int cpu);

include/xen/events.h

@@ -138,4 +138,7 @@ int xen_test_irq_shared(int irq);
 
 /* initialize Xen IRQ subsystem */
 void xen_init_IRQ(void);
+
+irqreturn_t xen_debug_interrupt(int irq, void *dev_id);
+
 #endif	/* _XEN_EVENTS_H */