spi: dt-bindings: cdns,qspi-nor: Deprecate the Cadence compatible alone

spi: dt-bindings: cdns,qspi-nor: Deprecate the Cadence compatible alone

The initial SPI controller IP from Cadence has always been implemented
into controllers from various hardware manufacturers and because of
that, it has always been (rightfully) doubled with a more specific
compatible. There are likely no reasons to keep this compatible
legitimate, alone. Make sure people do not get mislead by officially
deprecating this compatible.

While at deprecating, let's update the examples to avoid documenting
deprecated properties.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250319094651.1290509-3-miquel.raynal@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>