x86 PCI: Fix identity mapping for sandy bridge

x86 PCI: Fix identity mapping for sandy bridge

With SandyBridge, Intel has changed these Socket PCI devices to have a class
type of "System Peripheral" & "Performance counter", rather than "HostBridge".
So instead of using a "special" case to detect which devices will not be
doing DMA, use the fact that a device that is not associated with an IOMMU,
will not need an identity map.

Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Mike Habeck <habeck@sgi.com>