Move screen density config from PRODUCT_LOCALES to PRODUCT_AAPT_CONFIG

With this change, PRODUCT_LOCALES will contain only locales.
Other aapt config flags, such as *dpi, small/normal/large/xlarge,
should go to PRODUCT_AAPT_CONFIGS.
Bug: 4086309

Change-Id: I922f153d79777a9522c542a3907111193b40e7b7