x86: fold duplicate register printing code

What so far was OP_E_register() can be easily reused also for OP_G().
Add suitable parameters to the function and move the invocation of
swap_operand() to OP_E(). Adjust MOVSXD's first operand: There never was
a need to use movsxd_mode there, and its use gets in the way of the code
folding.