xen: events: pirq_check_eoi_map is X86 specific

On ARM I see:
drivers/xen/events.c:280:13: warning: 'pirq_check_eoi_map' defined but not used
[-Wunused-function]

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>