Add 2MB obtion to 8285 generic board (#7163)

The ESP8285H16 is reported to have 2MB of flash, so add an option the
the Generic 8285 board for 2MB.

Fixes #7161

package/package_esp8266com_index.template.json

@@ -378,4 +378,4 @@
          ]
       }
    ]
-}
+}