[non-BE] [allow-regression] Back and forth scaling in core decoder - non-BE

• Related issues: #2393
• Requested reviewers:

Reason why this change is needed

• The core coder suffers from unnecessary back-and-forth scaling of buffers

Description of the change

• Remove unnecessary scaling
• Remove unnecessary buffers:
  • Word16 output_16_fx[CPE_CHANNELS][L_FRAME48k];
  • Word16 save_hb_synth_fx_arr[L_FRAME48k];
  • Word16 synth_fxl[960];
  • => lowers decoder stack by 7,680 bytes
• Activation of non-BE back-and-forth scalings under FIX_2280_REDUCTION_UNNECESSARY_SCALING_NONBE

Affected operating points

• Not BE but buffers hold values with uncompromised precision.