virgl: Apply integer op fix only for ALU ops and clear modifiers

For texture fetches and buffer load the fix is not needed, and the override creates faulty TGSI.

In addition remove all modifiers from the src in the additional mov instruction.

Fixes: d1c7a7b1 virgl: Add an extra mov for int outputs from constant and immediate inputs

That fix was a bit sloppy, and the GLES deqp didn't have any test catching this.