FX Operand

This is an f32 or f16 operand depending on instruction modifiers:

Operand size is controlled by :ref:`m_op_sel_hi<amdgpu_synid_mad_mix_op_sel_hi>`.
Location of 16-bit operand is controlled by :ref:`m_op_sel<amdgpu_synid_mad_mix_op_sel>`.