aco: move src1 to vgpr instead of using VOP3 for VOP2 instructions during isel

Is simpler and helps a couple of shaders.
Totals from affected shaders: (Vega)
Code Size: 16341296 -> 16335460 (-0.04 %) bytes

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4642>
1 file changed