[AMDGPU] Allow folding to FMAMK with SGPR and immediate operand on GFX10+ (#72258)

Allow foldImmediate to create instructions like:

  v_fmamk_f32 v0, s0, 0x42000000, v0

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.