Add support for /product-services partition.

This CL is largely and adaptation of
Ie996def20e25dc1afe0c74af2096af844934b2dc

Bug: 80741439
Test: Successfully built product-services.img with one module in it, and
flashed on device. Also successfully built image with
/system/product-services and no dedicated /product-services partition.

Change-Id: I1046dfe19bf874da929c9131b76a1f85422fbb80
Merged-In: I1046dfe19bf874da929c9131b76a1f85422fbb80