fs_config: add product and product_services

Mechanical extension of mount directories to also support product/
and product_services/ as individually supplied images.

NB: In the distant past, a prototype placing the make rules into a
    macro was rejected as too difficult to maintain within the macro
    rules, so rules are rolled-out to make them easy to understand.

Test: compile
Bug: 119310326
Change-Id: Ief137cbe62db7175ee02275804ff1d644858dc3d