Add mcu_config_cache attribute to platform class

Author: Jason2866

platform.py

@@ -219,6 +219,7 @@ def __init__(self, *args, **kwargs):
         self._packages_dir = None
         self._tools_cache = {}
         self._mcu_cache = {}
+        self._mcu_config_cache = {}
         self._penv_python = None
         self._esptool_path = None