spi: dt-bindings: Convert marvell,orion-spi to DT schema

Convert the Marvell Orion SPI binding to schema.

Update compatible strings to what is in use. Generally,
"marvell,orion-spi" is a fallback compatible, but newer variants only
use "marvell,armada-380-spi".

Mark cell-index as deprecated and not required as some instances don't
use it already.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250702222643.2761617-1-robh@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>