atsamd: Implement custom memory allocation functions

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/atsamd/main.c

@@ -10,6 +10,22 @@
 
 DECL_CONSTANT(MCU, CONFIG_MCU);
 
+// Return the start of memory available for dynamic allocations
+void *
+dynmem_start(void)
+{
+    extern uint32_t _ezero;
+    return &_ezero;
+}
+
+// Return the end of memory available for dynamic allocations
+void *
+dynmem_end(void)
+{
+    extern uint32_t _sstack;
+    return &_sstack;
+}
+
 void
 command_reset(uint32_t *args)
 {