I didn’t have to make any changes specifically. But I made change to add sound/soc/hisilicon/hisi-i2s-plat.c to Makefile. With that I was able to see /snd/dev/xxxxx - both I2S devices.
Later I added changes to support saving parameters for multiple I2S devices which is about changing following fields in struct hisi_i2s in sound/soc/hisilicon/hisi-i2s.c
to array and corresponding changes.