drm/udl: drop use of drmP.h

The drmP.h header file is deprecated.
Drop it from all files in the udl driver.

Made the header files self contained, which then
made it simpler to update the .c files.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Robert Tarasov <tutankhamen@chromium.org>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Eric Anholt <eric@anholt.net>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Emil Lundmark <lndmrk@chromium.org>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190716064220.18157-9-sam@ravnborg.org