[SLOF] xhci in slof issues

[Dinar Valeev]

Hi,

While trying to fix my usb over vnc automated issues, I switched to
xhci, which helped a lot OS wise, but I see a regression in SLOF.

As you can see [1] we want to type an install repo url.  But at some
point capitalization of some characters are lost. Nope
openSUsE-tumbleweed instead of openSUSE-Tumbleweed.

I was able to reproduce it even with simpler testcase by using vncdotool

qemu-system-ppc64 -machine usb=off -vga std -enable-kvm -vnc :60 -m
4096 -device nec-usb-xhci -device usb-tablet -device usb-kbd

cat vnc.sh
vnc="vncdotool -s shiraz.arch:60"
$vnc type "HaHaHaHaHaHaHaHaHa"
$vnc key enter

while true;do ./vnc.sh;done

Three iterations are fine, starting with fourth characters are dropped.

[1] https://openqa.opensuse.org/tests/150621/modules/bootloader_ofw/steps/7