ivas_spar_com.c contains also other than SPAR functions

The source file ivas_spar_com.c contains other than SPAR functions too. It should be corrected as follows:

• ivas_get_twid_factors() -> move to ivas_mdct_imdct.c and define it as static
• ivas_get_mdct_scaling_gain() -> move to ivas_mdct_imdct.c and define it as static
• ivas_lfe_lpf_select_filt_coeff() -> move to a new file lib_com/ivas_lfe.c
• lfe_window_init() -> move to a new file lib_com/ivas_lfe.c and rename it to ivas_lfe_window_init()
• rename function LFE_tdplc() to ivas_lfe_tdplc()