Missing Half/Bfloat16 support in portable kernels

[manuelcandales]

🕵️‍♂️ Detected with FACTO

Ops with missing Half/Bfloat16 support:
✅ bmm.default
✅ convolution.default
✅ div.Scalar
✅ div.Tensor
✅ le.Scalar
✅ max.dim
✅ min.dim
✅ scatter_add.default
✅ native_group_norm.default

cc @larryliu0820