x86/apic: Move ipi header into apic directory

Only used locally.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190722105219.434738036@linutronix.de

arch/x86/kernel/apic/apic_numachip.c

@@ -18,7 +18,8 @@
 
 #include <asm/apic_flat_64.h>
 #include <asm/pgtable.h>
-#include <asm/ipi.h>
+
+#include "ipi.h"
 
 u8 numachip_system __read_mostly;
 static const struct apic apic_numachip1;