spi: dt-bindings: cadence: add soc-specific compatible strings for zynqmp and versal-net

spi: dt-bindings: cadence: add soc-specific compatible strings for zynqmp and versal-net

When the binding for the Cadence spi controller was written, a dedicated
compatible was added for the zynq device. Later when zynqmp and
versal-net, which also use this spi controller IP, were added they did
not receive soc-specific compatibles. Add them now, with a fallback to
the existing compatible for the r1p6 version of the IP so that there
will be no functional change. Retain the r1p6 in the string, to match
what was done for zynq.

Disallow the cdns,spi-r1p6 compatible in isolation to "encourage" people
to actually add soc-specific compatible strings in the future.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Link: https://patch.msgid.link/20251001-basics-grafting-a1a214ef65ac@spud
Signed-off-by: Mark Brown <broonie@kernel.org>