drm/mcde: More devm_drm_dev_init

Auto-unwind ftw, now possible with the fixed drm_device related
management.

Aside, clk/regulator seem to be missing devm versions for a bunch of
functions, preventing a pile of these simpler drivers from outright
losing their ->remove hook.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-34-daniel.vetter@ffwll.ch