Hello karthik AS,
Thank you for your question.
The current KSDK USB stack supports both high speed (EHCI) and full speed (KHCI).
As long as the board is capable of both EHCI and KHCI, e.g. twrk65f180m, you can build the target for EHCI or KHCI.
These changes need to be modify by the corresponding macros defined in USB Stack Configuration, usb_device_config.h
For full speed device KHCI
/*! @brief KHCI instance count */
#define USB_DEVICE_CONFIG_KHCI (1U)
/*! @brief EHCI instance count */
#define USB_DEVICE_CONFIG_EHCI (0U)
For high speed device EHCI
/*! @brief KHCI instance count */
#define USB_DEVICE_CONFIG_KHCI (0U)
/*! @brief EHCI instance count */
#define USB_DEVICE_CONFIG_EHCI (1U)
To your second question please refer to How to set the clock of desired frequency? here was the same question discussed.
Best Regards,
Iva