[AArch64] Use the reciprocal estimation machinery

This patch adds support for estimating the square root, its reciprocal and
division or reciprocal using the combiner generic reciprocal machinery.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268539 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed