Remove duplicated code: core-coder common update functions

The core-coder duplicates several common update functions. This issue is to track the removal of duplications in functions such as:

• updt_enc_common_fx() vs. updt_enc_common_ivas_fx()
• updt_dec_common_fx() vs. ivas_updt_dec_common_fx()
• updt_bw_switching_fx() vs. ivas_updt_bw_switching_fx()