dt: Add vendor prefix 'shimafuji'

Add Shimafuji Electric, Inc. to the list of device tree vendor
prefixes

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rob Herring <robh@kernel.org>