drm: Add devm_drm_dev_init()

This adds a resource managed (devres) version of drm_dev_init().

v2: Remove devm_drm_dev_register() since we can't touch hw in devm
    release functions and drivers want to disable hw on driver module
    unload (Daniel Vetter, Greg KH)

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190225144232.20761-3-noralf@tronnes.org