The 2 Mbits memory map information for ADSP-21488 automotive part is available under "Table 3. Internal Memory Space (2 MBits—ADSP-21488 Automotive Products Only)"(Page No: 6/71) in the latest ADSP-2148x datasheet Rev.I. This information will be available from the datasheet Rev.I. The link is given below.
https://www.analog.com/media/en/technical-documentation/data-sheets/adsp-21483_21486_21487_21488_21489.pdf