fatcat: Add initial mainboard support

This patch adds minimal code from rex to fatcat.

TODO: Add placeholder for TPM, Audio etc. as applicable based
on fatcat schematics.

BUG=b:347669091
TEST=Able to build fatcat depthcharge.

Change-Id: I62936719e8f6c454940b2a3f689cf1a3e941b5d7
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/depthcharge/+/5644377
Commit-Queue: Subrata Banik <subratabanik@chromium.org>
Reviewed-by: YH Lin <yueherngl@chromium.org>
Tested-by: Subrata Banik <subratabanik@chromium.org>
5 files changed