This 8-point Type-IV DST uses the same computation graph as the
 asymmetric 8-point Type-IV DST with the following changes:

  - The fDST and iDST contain different multiplication constants
  - The fDST does not reuse the passed shifts in the first additions
  - The iDST does not have any OD_RSHIFT1(t_) on the last additions

This reused computation structure could be later pulled into a macro or
 exploited by a hardware implementation.

Change-Id: Iac09c29549ce5dcf7752f71e9e6d24609e7b018a