mb/lenovo: add Lenovo ThinkPad X131e (Intel)

mb/lenovo: add Lenovo ThinkPad X131e (Intel)

The Intel version of ThinkPad X131e can ship with Sandy Bridge or
Ivy Bridge processors.  The mainboard uses 8MiB+4MiB flash chips, with
the 8MiB chip containing the IFD and ME, and the 4MiB chip containing
the BIOS.  The flash chips can be accessed with an external programmer.

This port was primarily created using autoport, with some parts adapted
from lenovo/x230 and google/stout.

Tested and working:
 - Machine type 3367AH5 / Intel Celeron 887 (Sandy Bridge)
 - Boots Debian GNU/Linux 9.2 (Linux 4.9.51) via SeaBIOS
 - Boot from internal SATA and USB
 - Native RAM init
 - Native VGA init
 - libgfxinit
 - VGA and HDMI display output
 - Keyboard, trackpoint, touchpad
 - Audio (speaker, headphones)
 - Ethernet (Realtek)
 - Display backlight
 - USB 3.0 ports
 - "Always on" USB port (EHCI debug)
 - SD card reader
 - Webcam
 - Fan and temperature sensors
 - ACPI S3 (Sleep)
 - CMOS
 - TPM

Not tested:
 - WLAN/Bluetooth (Broadcom)
 - WWAN/mSATA (no card)
 - Other operating systems

Not working or not implemented:
 - Fn keys
 - ACPI S4 (Hibernation) "Image mismatch: memory size"

Change-Id: If8de3a9308997e2d57aee869023ee9a43a2db872
Signed-off-by: James Ye <jye836@gmail.com>
Reviewed-on: https://review.coreboot.org/20694
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>