mainboard/lenovo: Add ThinkCentre M710s (Skylake)

mainboard/lenovo: Add ThinkCentre M710s (Skylake)

The processor may be a Pentium or 6/7th generation Core i3/i5/i7.
This port was tested on an i5-7400.

Working:
 - Can boot Ubuntu 22.04.1 (Linux 6.5.0) using payloads:
   - SeaBIOS
   - TianoCore EDK 2
 - Internal flashing (from coreboot)
 - PEG
 - PCIe
 - SATA
 - M.2 SSD
 - M.2 WLAN (+ Bluetooth)
 - LAN
 - USB
 - Memory card reader
 - CPU fan
 - VGA (DP bridge)
 - Display ports
 - Audio (output)
 - COM1
 - TPM

Not Working:
 - SuperIO related things
 - Power button LED
 - PCIe clock related things and AER issues (LiveCD)
 - Some drm issue when using EDK 2 and libgfxinit (LiveCD)
 - ME cleaner

Untested:
 - Audio (input)

Won't Test:
 - COM2 header
 - LPT header
 - PS/2 keyboard and mouse

Thanks to Nico Huber and everyone else on the IRC for helping me write
my first port!

Change-Id: I551753aecfbd2c0ee57d85bb22cb943eb21af3cc
Signed-off-by: Nicholas Sudsgaard <devel+coreboot@nsudsgaard.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80343
Reviewed-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>