Adds welltech,epbx100 as a valid intel-ixp4xx board.

Link: https://lore.kernel.org/r/20210504193457.4008384-5-clabbe@baylibre.comSigned-off-by: Corentin Labbe <clabbe@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Olof Johansson <olof@lixom.net>