[AIROCMLIR-199] Fix invalid chipset error on multi-GPU systems

[djramic]

Motivation

Resolve https://amd-hub.atlassian.net/browse/AIROCMLIR-199

Technical Details

• Multi-GPU detection in all lit.site.cfg.py.in files — when multiple architectures are found, config.multi_gpu_detected is flagged and config.arch is set to device 0's architecture.
• When multi-GPU is detected and the user hasn't set HIP_VISIBLE_DEVICES, it's automatically set to '0' in the test environment.
• User-specified HIP_VISIBLE_DEVICES is always respected.

Test Plan

Verify tests on system with multiple gpus.

Test Result

All tests are passing

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.