[Codegen] Fix ConvertAccGemmToGemm to handle read-write arguments correctly. (#22975)

The current pass unconditionally converts from an accumulating GEMM to a
non-accumulating GEMM. This transformation is only required when the
`outs` arguments is coming from a read-only buffer. When coming from a
read-write buffer, the accumulating gemm can be handled as is, and it
does not need to converted to a non-accumulating gemm.

For a function input like

```
func.func @acc_gemm(%lhs : tensor<?x?xf32>, %rhs: tensor<?x?xf32>,
    %init : tensor<?x?xf32> {iree.abi.output = 0}) -> tensor<?x?xf32> {
  %0 = linalg.matmul ins(%lhs, %rhs : tensor<?x?xf32>, tensor<?x?xf32>)
      outs(%init : tensor<?x?xf32>) -> tensor<?x?xf32>
  return %0 : tensor<?x?xf32>
}
```

The dispatch sees an single `init` binding that is read-write. In those
cases we dont need to convert the `linalg.matmul` into a
non-accumulating GEMM. This case can be (and is currently) handled
natively.

ci-extra: test_torch

---------

Signed-off-by: MaheshRavishankar <mahesh.ravishankar@gmail.com>