arm32 backend stuff needed to support IR artefacts resulting from

arm32 backend stuff needed to support IR artefacts resulting from
guest support of 32-bit V8 crypto instructions:

* add new pseudo-instruction ARMin_VXferQ, to move values between
  two D regs and a Q reg, in either direction.  Use this to implement
  Iop_64HLtoV128 much more efficiently than before, and to implement
  Iop_V128HIto64 and Iop_V128to64.

* Generate code for helper calls in which have four or more
  (32-bit) word-sized arguments and a V128 return value.
  These require passing arguments on the stack.

git-svn-id: svn://svn.valgrind.org/vex/trunk@3235