[AMDGPU] Allow folding to FMAAK with SGPR and immediate operand on GFX10+ (#72266)

Allow foldImmediate to create instructions like:

  v_fmaak_f32 v0, s0, v0, 0x42000000

This instruction has two "scalar values": s0 and 0x42000000. On GFX10+
this is allowed. This fold was originally implemented before the
compiler supported GFX10, when all ASICs were limited to one scalar
value.