Add 'ml.p5.48xlarge' as a supported instance for SM_EFA_NCCL_INSTANCES.

[andjsmi]

Describe the feature you'd like
Add "ml.p5.48xlarge" to the list of SM_EFA_NCCL_INSTANCES. This means SageMaker Training Toolkit sets FI_PROVIDER=efa automatically for use in training jobs to ensure EFA is used.

How would this feature be used? Please describe.
Automatically setting EFA for use in SageMaker Training Jobs that leverage the SageMaker Training Toolkit

Describe alternatives you've considered
Unsure. Currently you would manually set the environment variable.

Additional context
NA