x86: x86_32 has its own irq_regs definition

Impact: cleanup

Arches that have their own irq_regs definition are expected to
define ARCH_HAS_OWN_IRQ_REGS or else a generic (unused) set
will also be defined in lib/irq_regs.c

Sparse noticed the unused generic one had no prototype:
lib/irq_regs.c:15:1: warning: symbol 'per_cpu____irq_regs' was not declared. Should it be static?
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/irq_regs_32.h

@@ -9,6 +9,8 @@
 
 #include <asm/percpu.h>
 
+#define ARCH_HAS_OWN_IRQ_REGS
+
 DECLARE_PER_CPU(struct pt_regs *, irq_regs);
 
 static inline struct pt_regs *get_irq_regs(void)