drm/tinydrm/repaper: Drop using tinydrm_device

Use devm_drm_dev_init() and drop using tinydrm_device.

v2: devm_drm_dev_register() was dropped so add a driver release callback.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190225144232.20761-5-noralf@tronnes.org