drm/tinydrm: Drop driver registered message

No need to put out a driver registered message since drm_dev_register()
does that now. SPI speed is an important metric when dealing with
display problems, so retain that info.

Cc: David Lechner <david@lechnology.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: David Lechner <david@lechnology.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1504883250-43487-8-git-send-email-noralf@tronnes.org