ARM: dts: rmobile: Scrub unused DT nodes

Remove DT nodes which are not used by U-Boot, like audio and video in/out
nodes. This saves about 35 kiB on the resulting U-Boot binary without any
impact on functionality.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>