[CK] Add flag to enable library-only build

[mhalk]

Add '-l' flag to omit tests and examples during CK library build

Motivation

Tests and examples of CK are another point of failure during CK builds.
Also, this may save up on time (e.g. reducing the artifact count from 8k to 3k).

Technical Details

CK's CMake configuration uses GPU_ARCHS and GPU_TARGETS to distinguish between those build modes.
GPU_ARCHS omits tests & examples -AND- takes precedence over GPU_TARGETS.
See here: https://github.com/ROCm/composable_kernel/blob/develop/CMakeLists.txt#L209-L211

Test Plan

Manually ran CI test partially to confirm changed number of build steps with -l flag being set.

[mhalk]

Thanks for the prompt approval, I'll merge when I see that our (CK examples-related) build fail can be remedied with this :)