[M] Change in coreboot[main]: mb/google/skywalker: Add MediaTek MT8189 reference board

[Yidi Lin (Code Review)]

Attention is currently required from: Hung-Te Lin, Vince Liu.

Yidi Lin has posted comments on this change by Vince Liu. ( https://review.coreboot.org/c/coreboot/+/85617?usp=email )

Change subject: mb/google/skywalker: Add MediaTek MT8189 reference board
......................................................................

Patch Set 2: Code-Review+2

(1 comment)

Patchset:

PS2: 
You probably need to rebase to the latest main branch.
```
Traceback (most recent call last):
  File "/home/coreboot/node-root/workspace/coreboot-gerrit/./util/mtkheader/gen-bl-img.py", line 89, in <module>
    main(sys.argv)
  File "/home/coreboot/node-root/workspace/coreboot-gerrit/./util/mtkheader/gen-bl-img.py", line 86, in main
    write(argv[4], gen_preloader(argv[1], argv[2], read(argv[3])))
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/coreboot/node-root/workspace/coreboot-gerrit/./util/mtkheader/gen-bl-img.py", line 72, in gen_preloader
    gfh_info = gen_gfh_info(chip_ver, data)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/coreboot/node-root/workspace/coreboot-gerrit/./util/mtkheader/gen-bl-img.py", line 32, in gen_gfh_info
    load_addr = entries[chip] - gfh_size
                ~~~~~~~^^^^^^
KeyError: 'mt8189'
make[2]: *** [src/soc/mediatek/mt8189/Makefile.mk:22: /cb-build/coreboot-gerrit.0/gcc/GOOGLE_SKYWALKER/cbfs/fallback/bootblock.bin] Error 1
make[2]: Leaving directory '/home/coreboot/node-root/workspace/coreboot-gerrit'
```