[mlir][test] Fix linking error post test-lower-to-nvvm

[mlir][test] Fix linking error post test-lower-to-nvvm

This fixes builds for 7e78ecfe10ea9071234de8d385b87d338d280266 (both cmake and bazel) as well as trim unnecessary dependencies.

This is achieved by moving the functionality to test/lib/GPU which is a more natural landing pad.