uvm_reg/uvm_mem create functions

[jeiler]

Is there a reason that none of the classes for uvm_reg/uvm_mem stuff implement a create function?

A bunch of them extend uvm_object, so I think they should define a basic create function that returns a new object as opposed to falling through to the uvm_object::create function that just returns null.

[jadec]

These base classes are not intended to be directly instantiated.