[dev-alloc] Removing bitsPerElement parameter from alloc APIs.

[fasiddique]

I am wondering do we actually need the bitsPerElement parameter in the allocation APIs. Can we not just derive it from the data type?

[deyuan]

For functional simulation, we can derive bitsPerElement based on data types. The APIs can be simplified.
For micro-ops level simulation, it would be good to keep to flexibility for advanced usage.

[deyuan]

Closed with PR #168