kmsro: Add "mcde" entry point

kmsro: Add "mcde" entry point

ST-Ericsson Ux500 boards use a Mali 400 GPU together with MCDE
("Multi Channel Display Engine"), which is supported by the "mcde"
DRM driver.

Adding an entry point for it in kmsro seems to be enough to make
Lima work - at least kmscube is working correctly.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3139>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3139>