spi: mediatek: add set_cs_timing support

this patch add set_cs_timing support for HW CS mode.

Signed-off-by: leilk.liu <leilk.liu@mediatek.com>
Link: https://lore.kernel.org/r/20210207030953.9297-4-leilk.liu@mediatek.com


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