When you are in Suspend Mode, several Peripherals are removed from power and Clocks, this is the case of the EPDC, I don´t see a mode to prevent that EPDC does not go to sleep in the OCRAM only. Because it is part of the periheral. You will need to maitain on the complete EPDC. To keep a live the OCRAM of the EPDC.
Hope this clarifies.