[2.0.x] Teensy 3.1 and 3.2 support (#11460)

Marlin/src/HAL/shared/backtrace/unwmemaccess.cpp

@@ -84,6 +84,17 @@
 #define END_FLASH_ADDR    0x08100000
 #endif
 
+#ifdef __MK20DX256__
+// For MK20DX256 in TEENSY 3.1 or TEENSY 3.2
+//  SRAM  (0x1FFF8000 - 0x20008000) (64kb)
+//  FLASH (0x00000000 - 0x00040000) (256kb)
+//
+#define START_SRAM_ADDR   0x1FFF8000
+#define END_SRAM_ADDR     0x20008000
+#define START_FLASH_ADDR  0x00000000
+#define END_FLASH_ADDR    0x00040000
+#endif
+
 #ifdef __MK64FX512__
 // For MK64FX512 in TEENSY 3.5
 //  SRAM  (0x1FFF0000 - 0x20020000) (192kb)