Separate the concept of having memory access in operand 4 from the concept of having...

Separate the concept of having memory access in operand 4 from the concept of having the W bit set for XOP instructons. Removes ORing W-bits in the encoder and will similarly simplify the disassembler implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147366 91177308-0d34-0410-b5e6-96231b3b80d8