dt-bindings: display: Convert ingenic,lcd.txt to YAML

Convert the ingenic,lcd.txt to a new ingenic,lcd.yaml file.

In the process, the new ingenic,jz4780-lcd compatible string has been
added.

v2: Add info about IPU at port@8
v3: No change

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200716163846.174790-2-paul@crapouillou.net