spi: s3c64xx: introduce s3c64xx_spi_set_port_id()

Prepare driver to get rid of the of alias ID dependency. Split the
port_id logic into a dedicated method.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://msgid.link/r/20240216070555.2483977-9-tudor.ambarus@linaro.org


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