media: dt-bindings: mediatek,vcodec: Remove VDEC_SYS register space

The binding expects the first register space to be VDEC_SYS. However
this register space is already assigned to a different node on both
MT8173 and MT8183: a clock-controller node called 'vdecsys' which is
also a syscon.

In order to resolve the overlapping address ranges, remove the VDEC_SYS
register space from the video decoder, and add a new property to hold
the phandle to the syscon, so that iospace can still be handled.

Also add reg-names to be able to tell that this new register schema is
used, so the driver can keep backward compatibility.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>