kmsro: Add "mcde" entry point

Stephan Gerhold requested to merge Stephan/mesa:mcde into master

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.

Cc: @linusw

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