[OPT] improve rms_norm kernel

[kkHuang-amd]

Use vectorized memory access to improve rms_norm performance.

In the ROCm platform, we can do the 16 bytes memory access in one instruction, by using this instruction, we can do vectorized memory access for rms_nrom kernel.

From the testing, we can see rms_kernel has improvement

[gshtras]

@kkHuang-amd Could you please fill in a brief description of what this is doing, which improvement is expected and why

[HaiShaw]

LGTM

[gshtras]

Conditionally approving. My points of concern:

1. int32 for indices. Are we sure in this use case it won't cause overflows? cc @rasmith
2. Possible performance implications on platforms other than MI (Navi). cc @maleksan85

[rasmith]

Some places where integer overflow could occur.

[HaiShaw]

@rasmith Is this good now?

[rasmith]

@rasmith Is this good now?

Looks good!

The base branch was changed.

[gshtras]

Approved, pending conflict resolution

[HaiShaw]

LGTM

[gshtras]

@kkHuang-amd this PR introduces a correctness regression on Llama-3.2-90B-Vision-Instruct-FP8-KV model without triton flash attention.
I'm planning to revert it pending further investigation

[gshtras]

The issue is the following:
There used to be 2 versions of the kernel - MI and Navi.
After this PR, on MI the Navi version is called if vec_size is not a multiple of 8, which seems to be the case in the vision model. And this causes a correctness regression