[MIGraphX EP] Fix CreateExecutionProviderFactory with correct struct and change vendor_id (#25625)
This fixes the CreateIExecutionProvider for MIGraphX EP when calling
CreateExecutionProviderFactory, using OrtMIGraphXProviderOptions instead
of ProviderOptions.
Also changes the vendor_id so that OrderDevices in
provider_policy_context.cc will default dml ep when ep_policy is set to
GPU. Will update pending more changes to MIGraphX EP.
Co-authored-by: ozhang <ozhang@amd.com>