arm64: implement remaining SQDMULH and SQRDMULH cases.


git-svn-id: svn://svn.valgrind.org/vex@2911 8f6e269a-dfd6-0310-a8e1-e2731360e62c
Add a folding rule: XorV128(t,0) ==> t.


git-svn-id: svn://svn.valgrind.org/vex@2912 8f6e269a-dfd6-0310-a8e1-e2731360e62c
arm64: add support for: sqshl, uqshl, sqrshl, uqrshl (reg) (vector and scalar)


git-svn-id: svn://svn.valgrind.org/vex@2913 8f6e269a-dfd6-0310-a8e1-e2731360e62c