ac/nir: Fix gather4 integer wa with unnormalized coordinates

This adds a bit of unneccesary code on radeonsi, since whether
unnormalized coordinates are used is known at compile time with GL, but
I wasn't sure if it was worth the few instructions to plumb everything
through, especially for something so rare -- my shader-db doesn't have
any instances where this changes anything.

Fixes CTS tests I created at
https://github.com/cwabbott0/VK-GL-CTS/tree/unnorm-gather-tests
10 jobs for !1033 with review/ac-nir-gather-wa in 11 minutes and 25 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #343326
debian

00:00:29

 
  Build+Test
passed #343328
meson-clang

00:10:54

passed #343332
meson-clover

00:09:42

passed #343331
meson-main

00:08:50

passed #343327
meson-swr-glvnd

00:05:58

passed #343333
meson-vulkan

00:03:28

passed #343335
scons-llvm

00:04:00

passed #343334
scons-nollvm

00:03:39

passed #343329
scons-swr

00:07:24

passed #343330
scons-win64

00:07:43