don't put it in the install modules.
this works around a hanging issue on haswell thinkpads.
when any usb device is inserted, GRUB will sometimes
hang if started from the SeaBIOS payload, *while* the
USB device is plugged in.
plugging in the USB device after GRUB starts worked.
it will have to be investigated more at a later date,
but this simply configuration change works.
the xhci module is already loaded explicitly, in grub.cfg
Signed-off-by: Leah Rowe <leah@libreboot.org>
1b75d738bf