vfio passtrhough fails at 'No available IOMMU models' on Intel BDW-EP platform

Environment:
 ------------
 Host OS (ia32/ia32e/IA64): ia32e
 Guest OS (ia32/ia32e/IA64): ia32e
 Guest OS Type (Linux/Windows): linux
 kvm.git Commit: da3f7ca3
 qemu.git Commit: 38a762fe 
 Host Kernel Version: 4.4.0-rc2
 Hardware: BDW EP (Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz, Grantley-EP)

Bug description:
 --------------------------
 when create guest with vt-d assignment using vfio-pci driver, the guest can not be created.
Warning 'No available IOMMU models'


Reproduce steps:
 ----------------
 1. bind device to vfio-pci driver
 2. qemu-system-x86_64 -enable-kvm -m 512 -smp 2 -device vfio-pci,host=81:00.0 -net none -drive file=rhel7u2.qcow2,if=none,id=virtio-disk0 -device virtio-blk-pci,drive=virtio-disk0

Current result:
 ----------------
 qemu-system-x86_64: -device vfio-pci,host=81:00.0: vfio: No available IOMMU models
 qemu-system-x86_64: -device vfio-pci,host=81:00.0: vfio: failed to setup container for group 41
 qemu-system-x86_64: -device vfio-pci,host=81:00.0: vfio: failed to get group 41
 qemu-system-x86_64: -device vfio-pci,host=81:00.0: Device initialization failed

Expected result:
 ----------------
 guest can be created
Basic root-causing log:
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