drm/udl: Use devm_drm_dev_alloc

drm/udl: Use devm_drm_dev_alloc

With Thomas' patch to clean up fbdev init this is a rather standard
conversion to the new wrapper macro.

v2: Rebase on top of Thomas' patches to remove the return value from
drm_fbdev_generic_setup()

v3: Update commit message to reflect the reality of the rebased patch
(Sam)

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200415074034.175360-12-daniel.vetter@ffwll.ch