dt-bindings: display: add Unisoc's mipi dsi controller bindings

Adds MIPI DSI Controller
support for Unisoc's display subsystem.

v5:
  - Remove panel_in port for dsi node.

Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Signed-off-by: Kevin Tang <kevin.tang@unisoc.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211207142717.30296-6-kevin3.tang@gmail.com