Enable llama2 benchmarking with Turbine

[kuhar]

This is extension of the main Turbine refactoring work: #1931. To enable future performance-related work, we should recreate the 1.0 benchmarking mode from vicuna.py:

Enablement

• Allow llama2 to be run with a single prompt using a CLI script (@raikonenfnu)
• Port the benchmarking/statistics options from vicuna.py (e.g., setting the prompts, generating exactly K output tokens, running multiple iterations and reporting the averages, etc.)
• Add a README with benchmarking instructions

Correctness

• Make sure the output is human-readable with 7b/13b/70b on the targets of interest (gfx9, gfx11, and others)

Performance

• Add ukernel for argmax for ROCm GFX9 (@raikonenfnu)
• Add ukernel for argmax for ROCm GFX11 (@raikonenfnu)
• Add kernel for argmax for SPIR-V/Vulkan (@qedawkins)

[kuhar]

cc: @antiagainst @harsh-nod