bus/pci: support IOVA as VA in PowerVM LPARs

bus/pci: support IOVA as VA in PowerVM LPARs

Add IOMMU detection logic for PowerVM LPARs.

PowerNV $ cat /proc/cpuinfo
...
timebase     : 512000000
platform     : PowerNV
model        : 8335-GTW

PowerVM LPAR $ cat /proc/cpuinfo
...
timebase     : 512000000
platform     : pSeries
model        : IBM,9009-22A
machine      : CHRP IBM,9009-22A
MMU          : Hash

PowerNV KVM Guest $ cat /proc/cpuinfo
...
timebase     : 512000000
platform     : pSeries
model        : IBM pSeries (emulated by qemu)
machine      : CHRP IBM pSeries (emulated by qemu)
MMU          : Radix

Signed-off-by: David Christensen <drc@linux.vnet.ibm.com>
Reviewed-by: Thinh Tran <thinhtr@linux.vnet.ibm.com>