veyron: Initialize EC interrupt GPIO and add them to coreboot tables

veyron: Initialize EC interrupt GPIO and add them to coreboot tables

This patch initializes the GPIO for the Chrome EC interrupt line on
Veyron boards and passes its description through the coreboot table, so
that payloads with keyboard support can use it to detect pending key
presses.

BRANCH=none
BUG=chrome-os-partner:39514
TEST=Booted Jerry, confirmed that it could still detect keypresses.
Confirmed that EC log does not show a huge amount of MKBP polls.

Change-Id: I4de35ef411c3acc02282ebf8e764785a1e7bf6f1
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 8ad95d667ef3af3fb217e3c370468dc1d6ec36c9
Original-Change-Id: I8b426621af088460929cfff0a4b46618e2a86725
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/267344
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Original-Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: http://review.coreboot.org/10088
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>