chipset_enable: Add Kaby Lake U Prem. to known and tested systems

Intel Kaby Lake U (with the 9d4e device id) support is available but
marked not tested.

Tested reading, writing and erasing both internal flash chips on the
Facebook Monolith system with the Intel i3 7100U SoC. However, since all
ME-enabled chipsets are marked as DEP instead of OK, this one shall follow
suit as well.

Signed-off-by: Wim Vervoorn <wvervoorn@eltan.com>
Change-Id: Ie35cc896e29baffa63fe9e37c14770001b54e7ec
Reviewed-on: https://review.coreboot.org/c/flashrom/+/38481


Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>