spi: dt-bindings: cdns,qspi-nor: Move peripheral-specific properties out

spi: dt-bindings: cdns,qspi-nor: Move peripheral-specific properties out

The spi-peripheral-props.yaml schema contains peripheral-specific
properties for SPI controllers that should be present in the peripheral
node. Move peripheral-specific properties to a separate file and refer
to it in spi-peripheral-props.yaml.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211109181911.2251-3-p.yadav@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>