ivas_td_low_rate_dec converted to fixed point.

[x]Implemented td_low_rate_dec_fx and re-implemented
some EVS functions with IVAS specific processing
(disabled under ADD_LRTD macro).
[x]Examples:
- bands_and_bit_alloc_ivas_fx required conversion of
additional bit allocation processing
- GSC_gain_adj_ivas_fx required an additional gain
factor from IVAS code
- highband_exc_dct_in_ivas_fx required addition of
scaling code
- gsc_dec_ivas_fx required change in one of the if
conditions which was causing bit reading issues and
also required addition of scaling code.