x86: increase MAX_APICS for very large x86-64 configs

Increase the maximum number of apics when running very large
configurations. This patch has no affect on most systems.

The patch has no effect on any 32-bit kernel. It adds ~4k to the size
of 64-bit kernels but only if NR_CPUS > 255.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/asm-x86/mpspec_def.h

@@ -17,10 +17,11 @@
 # define MAX_MPC_ENTRY 1024
 # define MAX_APICS      256
 #else
-/*
- * A maximum of 255 APICs with the current APIC ID architecture.
- */
+# if NR_CPUS <= 255
 #  define MAX_APICS     255
+# else
+#  define MAX_APICS   32768
+# endif
 #endif
 
 struct intel_mp_floating {