spi: dt-bindings: cdns,qspi-nor: Require some peripheral properties

spi: dt-bindings: cdns,qspi-nor: Require some peripheral properties

There are 5 mandatory peripheral properties. They are described in a
separate binding but not explicitly required. Make sure they are
correctly marked required and update the example to reflect this.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250319094651.1290509-4-miquel.raynal@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>