Indeed, there are some examples for USB + fatfs on KSDK 1.3 version that do not use any RTOS (they are BareMetal). You can give a look to these examples at: <KSDK_1_3_PATH>\examples\<BOARD>\demo_apps\usb\<DEVICE_OR_HOST>\msd\BM\<IDE>.
Indeed, there are some examples for USB + fatfs on KSDK 1.3 version that do not use any RTOS (they are BareMetal). You can give a look to these examples at: <KSDK_1_3_PATH>\examples\<BOARD>\demo_apps\usb\<DEVICE_OR_HOST>\msd\BM\<IDE>.