mb/lenovo/x200: Add ThinkPad X301 as a variant

It is similar to X200s, with U-series CPU, slightly different gpio
setup, no docking support, and no superio chip.

Tested:
    - CPU Core 2 Duo U9400
    - Slotted DIMM 4GiB*2 from samsung
    - Camera
    - pci-e slots
    - sata and usb2
    - libgfxinit-based graphic init
    - NVRAM options for North and South bridges
    - Sound
    - Thinkpad EC
    - S3
    - Linux 4.19.67-2 within Debian GNU/Linux stable, loaded from
      Linux payload (Heads) and Seabios.

TODO: repurpose and/or rename flag H8_DOCK_EARLY_INIT (introduced in
      CB:4294 ) for h8-using devices without a dock.

Change-Id: Ic6a6059ccf15dd2e43ed4fc490c1d3c36aa1e817
Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36093
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

Documentation/mainboard/index.md

@@ -72,6 +72,10 @@ The boards in this section are not real mainboards, but emulators.
 
 - [T410](lenovo/t410.md)
 
+### GM45 series
+
+- [X301](lenovo/x301.md)
+
 ### Sandy Bridge series
 
 - [T420](lenovo/t420.md)

Documentation/mainboard/lenovo/x301.md

@@ -0,0 +1,44 @@
+# Lenovo X301
+
+## Disassembly Instructions
+
+You must remove the following parts to access the SPI flash:
+
+![X301 with WSON8 chip replaced with SOIC8 chip](x301_kb_removed.jpg)
+
+* Battery pack
+* Keyboard
+
+Its [Hardware Maintenance Manual](https://download.lenovo.com/ibmdl/pub/pc/pccbbs/mobiles_pdf/43y9441.pdf) can be used as a guidance of disassembly.
+
+The WSON-8 flash chip (surrounded with red circle in the photo above,
+already replaced with a SOIC-8 one) sits under a piece of insulating
+tape. If solders between the chip and soldering pads fortunately
+overflows beside the chip as tiny tin balls attached to soldering pads,
+it will be possible to use a pomona 5250 clip to hold the chip, with
+its metal tips just attached to tin balls, thus connecting the chip to
+the programmer. Otherwise, it may be recommended to replace it with a
+SOIC-8 one (you might need to add the chip to the IFD VSCC list), as
+what is done in the photo.
+
+The vendor IFD VSCC list contains:
+    -MACRONIX_MX25L6405 (0xc2, 0x2017)
+    -WINBOND_NEX_W25X64 (0xef, 0x3017)
+    -ATMEL_AT25DF641 (0x1f, 0x4800)
+
+```eval_rst
+:doc:`../../flash_tutorial/ext_power`
+```
+Tested:
+    - CPU Core 2 Duo U9400
+    - Slotted DIMM 4GiB*2 from samsung
+    - Camera
+    - pci-e slots
+    - sata and usb2
+    - libgfxinit-based graphic init
+    - NVRAM options for North and South bridges
+    - Sound
+    - Thinkpad EC
+    - S3
+    - Linux 4.19.67-2 within Debian GNU/Linux stable, loaded from
+      Linux payload (Heads) and Seabios.