partner_gms: Stop relying on exported vars for ATV and Automotive targets

Flag PRODUCT_IS_ATV must be set for all ATV targets,
so Automotive targets can follow and adopt PRODUCT_IS_AUTO as well.
No need to export WITH_GMS_TV or WITH_GMS_CAR anymore.

Change-Id: I7f35e7fa731f7cee239aff03c99b83975abbb56e