Let us try to understand what is i7-3720QM for itself? To find out, we'll ask our good friend
ark.intel.com:
Important points: 4 (Quad) Core, 8 HTs, TDP 45W, DDR3/DDR3L 1333/1666MHz, GFX base FREQ 650MHz, GFX Device ID 0x0166 .
vBIOS (64KB) file pci8086,0166.rom does exist, so GFX wise Coreboot is supported. I guess, IVB FSP does support as well i7-3720QM, with built-in MRC algorithms for DDR3 (1.5V) and DDR3L (1.35V) 1333/1666MHz.
The only one thing here to take care of is new MCU to be entered in config: it is after all sku specific (new sku demands new MCU).
And one more important point, economy wise, this sku costs around $350 USD. If you do have these monies, IVB is 61% more PM efficient then its counterpart SNB (currently present in yout T420 laptop). :-)
Good Luck!
Zoran