Add timing data for ISE-supported devices

[wanda-phi]

This covers:

• prjcombine-virtex
• prjcombine-virtex2
• prjcombine-spartan6
• prjcombine-virtex4, which will needs to be treated as four mostly-distinct targets:
  • Virtex 4
  • Virtex 5
  • Virtex 6
  • Virtex 7

XC4000 and XC5200 are not included here, as they seem to use a different speed model.

It is not completely clear how to do this yet. It's possible we'll just end up parsing the .spd files, though we may want to investigate if there's any hopes of blackboxing the data out.