llama2 - FP16 - IR generation

[PhaneeshB]

• fix combine mlir for llama2 for fp16 IR generation by keeping deduplicating constant variable names using appropriate suffix for first llama and second llama
• needs to be tested for IR generation with int4 to see it doesn't break the generation flow for quantised IRs

[PhaneeshB]

Converted to draft till sanity check is done for int4 IR generation.