There are two reasons why VT-d is not supported.
The Thinkpad Edge E531 has a HM77 chipset, which does not support VT-d. Only their "business" and "workstation" lines (e.g. T530, W530) uses the QM77 chipset, which does support VT-d.
The Thinkpad Edge E531 has a socketed motherboard (which is a "good" thing, in general, and allows swapping out CPU's for better ones, etc).
The 3632QM rPGA package (as opposed to BGA--a.k.a. "soldered") does NOT support VT-d. If you want VT-d, you will have to upgrade to a minimum of 3720QM for socketed CPU's. However, see reason #1 for why it would not work in your laptop.