Like other buggy models that had their fixes [1], the touchscreen with
id 04f3:21b8 from ELAN Microelectronics needs the device-qualifier
quirk. Otherwise, it fails to respond, blocks the boot for a random
amount of time and pollutes dmesg with:

[ 2887.373196] usb 1-5: new full-speed USB device number 41 using xhci_hcd
[ 2889.502000] usb 1-5: unable to read config index 0 descriptor/start: -71
[ 2889.502005] usb 1-5: can't read configurations, error -71
[ 2889.654571] usb 1-5: new full-speed USB device number 42 using xhci_hcd
[ 2891.783438] usb 1-5: unable to read config index 0 descriptor/start: -71
[ 2891.783443] usb 1-5: can't read configurations, error -71

[1]: See commits c68929f7, 876af5d4, d7499475, a32c99e7 and dc703ec2.
Tested-by: NAdrien Vergé <adrienverge@gmail.com>
Signed-off-by: NAdrien Vergé <adrienverge@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>