x86: Tell irq work about self IPI support

x86 supports irq work self-IPIs when local apic is available. This is
partly known on runtime so lets implement arch_irq_work_has_interrupt()
accordingly.

This should be safely called after setup_arch().

Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Frederic Weisbecker <[e-mail]>

arch/x86/include/asm/Kbuild

···
 generic-y += clkdev.h
 generic-y += cputime.h
 generic-y += early_ioremap.h
-generic-y += irq_work.h
 generic-y += mcs_spinlock.h
 generic-y += scatterlist.h

arch/x86/include/asm/irq_work.h

···
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return cpu_has_apic;
+}
+
+#endif /* _ASM_IRQ_WORK_H */

arch/x86/kernel/irq_work.c

···
 void arch_irq_work_raise(void)
 {
 #ifdef CONFIG_X86_LOCAL_APIC
-	if (!cpu_has_apic)
+	if (!arch_irq_work_has_interrupt())
 		return;
 
 	apic->send_IPI_self(IRQ_WORK_VECTOR);