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>