grub2 - usb 3.0 support

[Oleg Gryb]

I've just installed usb 3.0 NEC card with my Linux 3.6.35.4 kernel and it 
worked 
fine with xhci_hcd driver, but Grub2 doesn't see the card and I can't boot from 
a flash drive because of that.

Apparently, my BIOS doesn't support usb 3.0 either. I've searched 
/usr/lib/grub/i386-pc directory with all grub modules and didn't see there 
anything related to xhci_hcd.

Please let me if you plan to add the modue to grub of if there is any other way 
around. I've tried to insmod all USB related modules through /etc/grub.d and 
mannually through grub shell but it didn't help.

The grub version that I'm using is 1.98.