vhdl-compose-create-files

vhdl-compose-create-files is a variable defined in `vhdl-mode.el'.
Its value is

single

Documentation:
Specifies whether new files should be created for the new component.
The component's entity and architecture are inserted:
None : in current buffer
Single file : in new single file
Separate files: in two separate files
The file names are obtained from variables `vhdl-entity-file-name' and
`vhdl-architecture-file-name'.

You can customize this variable.