[CostModel]Add cost model for experimental.vector.reverse

Authored by CarolineConcatto on Jan 27 2021, 7:59 AM.


[CostModel]Add cost model for experimental.vector.reverse

This patch uses the function getShuffleCost with SK_Reverse to compute the cost
for experimental.vector.reverse.
For scalable vector type, it adds a table will the legal types on
AArch64TTIImpl::getShuffleCost to not assert in BasicTTIImpl::getShuffleCost,
and for fixed vector, it relies on the existing cost model in BasicTTIImpl.

Depends on D94883

Differential Revision: https://reviews.llvm.org/D95603