Move partner androidmk and bpfix files to match their package path

Using a gomod-aware editor with build/soong requires that files
in build/soong can be mapped to the android/soong package path.
Move the partner androidmk and bpfix files such that their path
matches the package path when the android/soong package prefix is
replaced with the build/soong path prefix.

Test: go test ./...
Test: m bpfix androidmk partner_bpfix partner_androidmk
Change-Id: Ic7f7aad9e5eb9178eef0383f0b37e4fb93ce8314