Rename the vector subparts-of-lanes-reversal IROps to names
that are easier to understand.  No functional change.


git-svn-id: svn://svn.valgrind.org/vex@2890 8f6e269a-dfd6-0310-a8e1-e2731360e62c
arm64: implement: rbit 16b,8b, rev16 16b,8b


git-svn-id: svn://svn.valgrind.org/vex@2891 8f6e269a-dfd6-0310-a8e1-e2731360e62c