Add a way to override LOCAL_PRODUCT_MODULE.

This CL introduces the product variable
PRODUCT_FORCE_PRODUCT_MODULES_TO_SYSTEM_PARTITION, which can contain a
list of module names to be "unmarked" from being LOCAL_PRODUCT_MODULE.

If a module name is included in this variable and if that module is
declared as LOCAL_PRODUCT_MODULE, the setting will be overriden and the
module will be installed in /system. This is useful to control this
behavior on a device-specific level.

Test: m; and checked resulting output.
Bug: 110072687
Change-Id: Iaab663a7ed757c1dd4f16169b0ac3d71650014d2