esp32: Track allocated iRAM and free it on soft reset.

This makes sure all iRAM allocated for native code is freed on soft reset.

Signed-off-by: Damien George <damien@micropython.org>
diff --git a/ports/esp32/mpconfigport.h b/ports/esp32/mpconfigport.h
index a3e4acf..a64d6de 100644
--- a/ports/esp32/mpconfigport.h
+++ b/ports/esp32/mpconfigport.h
@@ -152,6 +152,7 @@
     mp_obj_t machine_pin_irq_handler[40]; \
     struct _machine_timer_obj_t *machine_timer_obj_head; \
     struct _machine_i2s_obj_t *machine_i2s_obj[I2S_NUM_MAX]; \
+    mp_obj_t native_code_pointers; \
     MICROPY_PORT_ROOT_POINTER_BLUETOOTH_NIMBLE
 
 // type definitions for the specific machine