spi: spi-fsl-lpspi: support multiple cs for lpspi

support to get chip select number from DT file.

Signed-off-by: Han Xu <han.xu@nxp.com>
Link: https://lore.kernel.org/r/20221206225410.604482-1-han.xu@nxp.com


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