x86, xen: fix hardirq.h merge fallout

Impact: build fix

This build error:

 arch/x86/xen/suspend.c:22: error: implicit declaration of function 'fix_to_virt'
 arch/x86/xen/suspend.c:22: error: 'FIX_PARAVIRT_BOOTMAP' undeclared (first use in this function)
 arch/x86/xen/suspend.c:22: error: (Each undeclared identifier is reported only once
 arch/x86/xen/suspend.c:22: error: for each function it appears in.)

triggers because the hardirq.h unification removed an implicit fixmap.h
include - on which arch/x86/xen/suspend.c depended. Add the fixmap.h
include explicitly.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/xen/suspend.c

@@ -6,6 +6,7 @@
 
 #include <asm/xen/hypercall.h>
 #include <asm/xen/page.h>
+#include <asm/fixmap.h>
 
 #include "xen-ops.h"
 #include "mmu.h"