MAINTAINERS: Move udl drm driver to drm-misc tree

Move udl maintenance into drm-misc tree. I've also signed up to be a
reviewer, but have kept it at Odd Fixes level of support.

Cc: Dave Airlie <airlied@redhat.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180919204026.3217-1-sean@poorly.run