libpayload: usb: xhci: Fix TD size if it overflows 5 bits

xHCI Spec says TD Size (5 bits) field shall be forced to 31,
if the number of packets to be scheduled is greater than 31.

BUG=chrome-os-partner:27837
BRANCH=rambi,nyan
TEST=Manual: Ensure recovery boot with USB 2.0 media on Squawks
works fine without any babble errors.

Original-Change-Id: Iff14000e2a0ca1b28c49d0da921dbb2a350a1bbd
Original-Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Original-Originally-Reviewed-on: https://chromium-review.googlesource.com/202297
Original-Reviewed-on: https://chromium-review.googlesource.com/202330
Original-Reviewed-by: Shawn Nematbakhsh <shawnn@chromium.org>
Original-Commit-Queue: Julius Werner <jwerner@chromium.org>
Tested-by: Julius Werner <jwerner@chromium.org>
(cherry picked from commit ae58b99370df3a86bf15d84b97db858a968b1dbd)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I9668b947f676c109fad9297e5efde91bf7f796fd
Reviewed-on: http://review.coreboot.org/7913
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>