dt-bindings: arm: Add Realtek RTD1295 bindings

The Zidoo X9S and a few other recent TV boxes feature the Realtek RTD1295,
a quad-core ARM Cortex-A53 SoC.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Roc He <hepeng@zidoo.tv>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>