libpayload: usb: xhci: set ENT flag in last Normal TRB

If a TD is comprised of one or more Normal TRBs and terminated with an
Event Data TRB, then the transition to the Idle state (and associated
Stream state save) could occur after all the data for the TD has been
moved (e.g. after Transfer Event TRBs have been executed), but before the
Event Data TRB is executed. Under these conditions, the execution of the
Event Data TRB is necessary to complete the TD, otherwise it does not
occur until the next time the Stream is scheduled. This could lead to the
lock up.

The Evaluate Next TRB(ENT) flag provides a means of forcing the execution
of a terminating Event Data TRB. Setting ENT flag in last Normal TRB makes
the xHC to evaluate the Even Data TRB.

BUG=chrome-os-partner:29375
TEST=Verified kernel boot-up on storm from previously failing USB stick.
     USB stick model: Sandisk Ultra USB 3.0 Pen Drive 32 GB
		      Strontium Jet USB 3.0 Pen Drive 32 GB

Change-Id: I092e2109c55c2274239c493cb67b47d730304ed2
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 7eefb3b2858c841165ae839d349d2a0be50fbcc8
Original-Change-Id: I4e123577ec5a5996d87d2fc52cb6cf5c571c9fae
Original-Signed-off-by: Sourabh Banerjee <sbanerje@codeaurora.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/220123
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Original-Commit-Queue: Vadim Bendebury <vbendeb@chromium.org>
Original-Tested-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: http://review.coreboot.org/8736
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

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