[rendering] refactor Crend interface to be independent of decoder struct

As part of external renderer development, several wrapper functions were added to be able to initialise Crend without the need to pass st_ivas / decoder struct, but instead only the necessary arguments, enabling use in the external renderer.

This ticket is to track the refactoring/harmonization of the functions in both the decoder and external renderer:

• ivas_crend_init_from_rom() and ivas_rend_initCrend()
• ivas_crend_open() and ivas_rend_openCrend()
• ivas_crend_process() and ivas_rend_crendProcess()
• ivas_crend_convolver() and ivas_rend_crendConvolver()

Ideally, the duplicated code can be removed and one set of functions used across the decoder and renderer.