Split st,stm32-fmc2-ebi.yaml specific properties into
st,stm32-fmc2-ebi-props.yaml, split memory-controller bus peripheral
properties into mc-peripheral-props.yaml, reference the
st,stm32-fmc2-ebi-props.yaml in mc-peripheral-props.yaml and reference
the mc-peripheral-props.yaml in micrel,ks8851.yaml.

This way, the FMC2 controller properties in Micrel KSZ8851MLL ethernet
controller node can be properly validated.

Fixes the following warning:
  arch/arm/boot/dts/stm32mp153c-dhcor-drc-compact.dtb: ethernet@1,0:
    Unevaluated properties are not allowed ('bank-width', 'st,fmc2-ebi-cs-mux-enable', ... 'st,fmc2-ebi-cs-write-data-hold-ns' were unexpected)
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20220928181944.194808-1-marex@denx.de
[krzk: trim warning message]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>