Hi Mrudula,
Now, I mainly support the RT and kinetis product, not the S32K144, so I also don't have your chip related driver.
But if you want to refer to the Kinetis SPI SD card driver, I attach it for your reference.
Wish it helps you!
But you need to modify the related SPI driver to your own chip driver, you need to make sure the chip SPI operation is correct, then add the SD card init, write, read etc, then add the fatfs.
Best Regards,
Kerry