dt-bindings: display: mcde: Convert to YAML schema

This moves the MCDE bindings over to using the YAML schema
to describe the ST-Ericsson MCDE display controller,
making use of the generic DSI controller schema.

In the process we correct an error in the old text bindings:
the clocks for the SDI host controllers were specified as
part of the main MCDE component while they should be
specified in the DSI host controller subnodes. This was
a leftover from an earlier iteration of the first patch
series adding the MCDE.

We also add the "port" node, we will use this when adding
LCD panels using the direct parallel interface DPI instead
of DSI.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20201115185145.566772-1-linus.walleij@linaro.org