libclc/r600: Use target specific builtins to implement rsqrt and native_rsqrt

Fixes OCL CTS rsqrt and half_rsqrt (1 thread, scalaer) tests on AMD Turks.

Reviewer: awatry
Differential Revision: https://reviews.llvm.org/D74016
GitOrigin-RevId: 85e2fa44c64e1edd2f675c990ecc60f5fadb4686
3 files changed