Please refer to the SPI timing diagrams (figure 10) in CX3 datasheet. From this, we can understand that DDR mode is not supported by CX3. Also, as you might be knowing the maximum operation frequency of SPI master of CX3 is 33MHz. Due to this the maximum interface speed with the flash will be 33MHz (even though the flash supports beyond this). So, both the flash parts S25FS128SAG and S25FS128SDS can be used with CX3 but in SDR mode only.