[ARM] Replace ARMISD::RBIT with ISD::BITREVERSE

ISD::BITREVERSE matches "rbit" completely, so remove ARMISD::RBIT and mark ISD::BITREVERSE as legal, adding a test for lowering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253047 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed