Hi Sidney,
In ADSP-21489 SPI master boot mode, the processor initiates the booting operation by activating the SPICLK signal and asserting the SPI_FLG0_O signal (used as the chip select for SPI Flash) to the active low state. By default the SPI_FLG0_O is connected to DPI Pin 05 of the processor. Hence, you can observe in the EZ-Kit that serial flash CS is connected to DPI_PB05. So I recommend you to make modification in your board such a way that connect the CS of the SPI flash to DPI_PB05, for the processor to boot from SPI Flash.
Thanks & Regards
Jithul