I recently had the pleasure to prepare a ADSP-21261 based device to boot in SPI flash master boot mode. The flash involved was SST Microchip's SPI serial flash SST25VF020B. DSP and SPI serial flash were connected as on the ADSP-21262 EZ-Kit Lite (SPI flash chip select via FLG0). For this I adapted the existing serial flash driver to support ADSP-21261 and added a driver implementation for the SST flash type (see 21261EzFlashDriver_Serial.zip in attachments).
Furthermore I wrote a python based production script which allows me to easily program my ADSP-device's serial flash via the Standalone Flash Programmer (contained in VisualDSP++, no license required). See attached WAdspSAFP.py, use python WAdspSAFP.py --help to see "manpage". Just thought I'd share this, obviously no liability assumed.