waf: rename EXTERNAL_PROG_FLASH_MB to EXT_FLASH_SIZE_MB

Tools/ardupilotwaf/chibios.py

@@ -237,8 +237,8 @@ class generate_apj(Task.Task):
             "flash_total": int(self.env.FLASH_TOTAL),
             "image_maxsize": int(self.env.FLASH_TOTAL),
             "flash_free": int(self.env.FLASH_TOTAL) - len(intf_img),
-            "extflash_total": int(self.env.EXTERNAL_PROG_FLASH_MB * 1024 * 1024),
-            "extflash_free": int(self.env.EXTERNAL_PROG_FLASH_MB * 1024 * 1024) - len(extf_img),
+            "extflash_total": int(self.env.EXT_FLASH_SIZE_MB * 1024 * 1024),
+            "extflash_free": int(self.env.EXT_FLASH_SIZE_MB * 1024 * 1024) - len(extf_img),
             "git_identity": self.generator.bld.git_head_hash(short=True),
             "board_revision": 0,
             "USBID": self.env.USBID