Define __ANDROID_VENDOR__ and __ANDROID_PRODUCT__

__ANDROID_VNDK__ is defined for the modules that are able to use the
VNDK libraries. As both product and vendor variants define
__ANDROID_VNDK__, we don't know if a module is built for vendor or
product on build time.

__ANDROID_VENDOR__ and __ANDROID_PRODUCT__ macros can be used to
specify the image-variant-dependent codes.

Bug: 180646847
Test: m nothing
Change-Id: Id6c3e1e3d47deaf3684c0c02964718658cf2fec5