Permit memory operands in ins/outs instructions

[x86] (PR15455) While (ins|outs)[bwld] instructions do not take %dx as a
memory operand, various unofficial references do and objdump
disassembles to this format. Extend special treatment of
similar (in|out)[bwld] operations.

Reviewers: craig.topper, rnk, ab

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18837

llvm-svn: 274152