x86/PCI: Allow x86 platforms to use translation offsets

The memory range descriptors in the _CRS control method contain an address
translation offset for host bridges.  This value is used to translate
addresses across the bridge.  The support to use _TRA values is present for
other architectures but not for X86 platforms.

For existing X86 platforms the _TRA value is zero.  Non-zero _TRA values
are expected on future X86 platforms.  This change will register that value
with the resource.

Signed-off-by: Mike Yoknis <mike.yoknis@hp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>