vc4: Allow TLB Z/color/stencil writes from any ALU operation in QIR.

vc4: Allow TLB Z/color/stencil writes from any ALU operation in QIR.

This lets us write the Z directly from the FTOI for computed Z, and may
let us coalesce color writes in the future.

No change in my shader-db, but clearly drops an instruction in piglit's
early-z test.