x86/apic: Consolidate the apic local headers

Now there are three small local headers. Some contain functions which are
only used in one source file.

Move all the inlines and declarations into a single local header and the
inlines which are only used in one source file into that.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190722105219.618612624@linutronix.de

arch/x86/kernel/apic/apic_numachip.c

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