Properly locate relocation position in instructions with immediate operands

[Maratyszcza]

Currently the code that detects relocation position in instructions with Constant operands assumes that disp32 is the last part of the encoding. This assumption does not hold if instruction has both a Constant operand and an immediate operand, which can happen e.g. in [V]CMPxx instructions. Need a more generic code to detect relocation position.