media: dt-binding: media: Add rk3568-vepu binding

The RK3568 and RK3566 have a Hantro VPU node solely dedicated to
encoding. This patch adds a new binding to describe it, as it
does not really fit the rockchip-vpu binding, since there is no
decoder.

Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>