[Android] Add hdpi to the build

In order to support hdpi in the device, you have to add hdpi to the makefile.

For example, in order to build a simulator that supports hdpi,

Edit generic.mk (under build/target/product).
Add the following lines at the end of the file.

PRODUCT_LOCALES := hdpi ...

You can add other configuration options like ko_KR en_US mdpi ldpi