Are you using a DSDT file at all?
I am using the same H77 chipset, not the same board, and did not have to add anything for the USB specifically.
I have a Toshiba 1tb USB3 drive that I have tested on both USB ports, and additionally tested against the USB2 ports. I have no problem with that drive at all (the only USB3 device I have on hand) and the OS accurately identifies the protocol of any other devices I plug into the USB3 ports.
I have tested speed as well to see the Toshiba drive runs ~3x faster on the USB3 ports than the USB2 so they are obviously being supported without any additional kext's or editing of anything.
**I am using an extracted/optimized DSDT file though.**
It would be a bummer if there was any difference in the mobile version. I have not seen any kexts or edits to provide USB3 specific support for the x77 chipset as ML already supports it..