[PATCH] x86_64: Port over e820 gap detection from i386

Look for gaps in the e820 memory map to put PCI resources in.

This hopefully fixes problems with the PCI code assigning 32bit BARs MMIO
resources which are >32bit.

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