[PATCH] x86_64: Fix memory hotadd heuristics

This fixes some boot failures on Dell and Unisys systems with memory
hotadd added.

 - Set hotadd_percent to 0 by default.  This means anybody using hotadd
   memory needs to specify the value on the command line.  That's
   because there are lots of Intel boxes which have a bogus hotplug area
   in their SRAT and they would waste a lot of memory before.
 - Fix calculation of how much memory to use when the hotplug area
   exceeds hotadd_percent
 - Fix fallback when the
 - Fix fallback if memory hotadd is not compiled in.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>