rp2: Add defaults for __micropy_flash_size__.

Signed-off-by: Dryw Wade <[email protected]>

Author: sfe-SparkFro

ports/rp2/CMakeLists.txt

@@ -525,11 +525,24 @@ target_compile_options(${MICROPY_TARGET} PRIVATE
 
 target_link_options(${MICROPY_TARGET} PRIVATE
     -Wl,--defsym=__micropy_c_heap_size__=${MICROPY_C_HEAP_SIZE}
-    -Wl,--defsym=__micropy_flash_size__=${PICO_FLASH_SIZE_BYTES}
     -Wl,--wrap=dcd_event_handler
     -Wl,--wrap=runtime_init_clocks
 )
 
+if(PICO_FLASH_SIZE_BYTES GREATER 0)
+    target_link_options(${MICROPY_TARGET} PRIVATE
+        -Wl,--defsym=__micropy_flash_size__=${PICO_FLASH_SIZE_BYTES}
+    )
+elseif(PICO_RP2040)
+    target_link_options(${MICROPY_TARGET} PRIVATE
+        -Wl,--defsym=__micropy_flash_size__=2048k # Default to 2MB
+    )
+elseif(PICO_RP2350)
+    target_link_options(${MICROPY_TARGET} PRIVATE
+        -Wl,--defsym=__micropy_flash_size__=4096k # Default to 4MB
+    )
+endif()
+
 if(PICO_RP2350)
     target_link_options(${MICROPY_TARGET} PRIVATE
         -Wl,--defsym=__micropy_extra_stack__=4096