mainboard/lenovo/x230: Add ThinkPad x230s as a variant

The code is based on autoport and that for X230. Major differences are:
    - Only one DDR3 slot
    - HM77 PCH
    - M.2 socket instead of mini PCIe
    - No docking
    - No TPM

Tested:
    - CPU i5-3337U
    - 8GiB SO-DIMM
    - Camera
    - PCIe and USB2 on M.2 slot with A key for WLAN
    - SATA and USB2 (no SuperSpeed components) on M.2 slot with B key for WWAN
    - On board SDHCI connected to PCIe
    - USB3 ports
    - libgfxinit-based graphics init
    - NVRAM options for North and South bridges
    - Sound
    - ThinkPad EC
    - S3
    - Linux 4.9 within Debian GNU/Linux stable, loaded from SeaBIOS.

Untested:
    - Touch screen, which is said to work under ubuntu but not debian.

Change-Id: Id59cdc5479aaf70809dd1ca613056263661455eb
Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41390
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/lenovo/x230/Kconfig.name b/src/mainboard/lenovo/x230/Kconfig.name
index 10fdc2e..1a01436 100644
--- a/src/mainboard/lenovo/x230/Kconfig.name
+++ b/src/mainboard/lenovo/x230/Kconfig.name
@@ -3,3 +3,6 @@
 
 config BOARD_LENOVO_X230T
 	bool "ThinkPad X230t"
+
+config BOARD_LENOVO_X230S
+	bool "ThinkPad X230s"