spi: s3c64xx: let the SPI core determine the bus number

Let the core determine the bus number, either by getting the alias ID
(as the driver forces now), or by allocating a dynamic bus number when
the alias is absent. Prepare the driver to allow dt aliases to be
absent.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://msgid.link/r/20240216070555.2483977-8-tudor.ambarus@linaro.org


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