phi2 contrib ops changes (#19112)
### Description
<!-- Describe your changes. -->
1. support causal mask in MHA cpu
2. support custom rotary_dim in rotary_emb
3. add bf16 for rotary_emb
4. fix a bug in attention rotary
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
