dt-bindings: display: Convert fsl,imx-fb.txt to dt-schema

dt-bindings: display: Convert fsl,imx-fb.txt to dt-schema

Compared to the txt description this adds clocks and clock-names to
match reality.

Note that fsl,imx-lcdc was picked as the new name as this is the actual
hardware's name. There will be a new binding implementing the saner drm
concept that is supposed to supersede this legacy fb binding

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221129180414.2729091-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Rob Herring <robh@kernel.org>