ports/rp2: Fix garbage collection with large heap.

Signed-off-by: Mike Bell <mdb036@gmail.com>

Author: MichaelBell

ports/rp2/mpconfigport.h

@@ -71,8 +71,16 @@
 #define MICROPY_CONFIG_ROM_LEVEL                (MICROPY_CONFIG_ROM_LEVEL_EXTRA_FEATURES)
 #endif
 
+#ifndef MICROPY_HW_ENABLE_PSRAM
+#define MICROPY_HW_ENABLE_PSRAM (0)
+#endif
+
 // Memory allocation policies
+#if MICROPY_HW_ENABLE_PSRAM
+#define MICROPY_GC_STACK_ENTRY_TYPE             uint32_t
+#else
 #define MICROPY_GC_STACK_ENTRY_TYPE             uint16_t
+#endif
 #ifndef MICROPY_GC_SPLIT_HEAP
 #define MICROPY_GC_SPLIT_HEAP                   (0) // whether PSRAM is added to or replaces the heap
 #endif