By default the heap is declared to be of size 0x2000 bytes and is located in the linker section .heap which is placed in the MEM_L3 memory section.To replace the system heap, an instance of the heap object should be added to the application.
For example : To declare a heap of 0xA000 bytes
#include <stdint.h>
uint8_t __adi_heap_object[0xA000] __attribute__ ((section (".heap")));
Also please refer below CCES help path for more information:
CrossCore
Embedded Studio 2.x.x > ARM Development Tools Documentation > Cortex-A > Analog Devices ARM Toolchain Manual > Appendix A - Application Guidelines > Managing the Heap for ADSP-SC5xx ARM Cores