UBSAN overflow in FFT

An overflow in the fft was observed for certain configurations. The root cause was in the scaling of the fft input data in dct_IV and dst_IV.
The following patch revises the scaling in dct and removes the unused arm implementation.

Bug: 112661057
Bug: 109936783
Bug: 112022208
Test: atest DecoderTestXheAac ; atest DecoderTestAacDrc
Change-Id: Idc9c44a9755b8151d5c7d8107696f43ac592413b
2 files changed