In STA mode ast idx override approach is used. In DSc to use ast idx
Need to configure a search idx register with ast idx and cache set number.
Added needed logic to instantiate search index register and
use it for STA mode in DSC path.
Change-Id: I6b3fb7c01a39b16ff1d473381c6155436fe2b27a
CRs-Fixed: 3375219