There are some machines around (large xSeries or Unisys ES7000) that
need physical IO-APIC destination mode to access all of their IO
devices. This currently doesn't work in UP kernels as used in
distribution installers.

This patch allows to compile even UP kernels as GENERICARCH which
allows to use physical or clustered APIC mode.

Signed-off-by: Andi Kleen <ak@suse.de>