nouveau: Support nir_intrinsic_*_atomic_fadd

This fixes failures in piglit's nv_shader_atomic_float tests with
NV50_PROG_USE_NIR=1
35 jobs for !9866 with atomic_fadd in 57 seconds (queued for 4 seconds)
detached
Status Job ID Name Coverage
  Sanity
passed #8349319
sanity

00:00:57

 
  Container
manual #8349322
aarch64 manual
arm_build
manual #8349323
manual
arm_test-base
manual #8349324
windows shell 1809 mesa manual
windows_build_vs2019
manual #8349320
manual
x86_build-base
manual #8349321
manual
x86_test-base
 
  Container 2
created #8349332
android_build
created #8349335
arm64_test
created #8349336
armhf_test
created #8349329
i386_build
created #8349325
kernel+rootfs_amd64
created #8349326
aarch64
kernel+rootfs_arm64
created #8349327
aarch64
kernel+rootfs_armhf
created #8349330
ppc64el_build
created #8349331
s390x_build
created #8349328
x86_build
created #8349333
x86_test-gl
created #8349334
x86_test-vk
 
  Meson X86 64
created #8349342
meson-clang
created #8349343
meson-clover
created #8349339
meson-clover-testing
created #8349340
meson-gallium
created #8349341
meson-release
created #8349337
meson-testing
created #8349338
meson-testing-asan
created #8349344
meson-vulkan
 
  Build Misc
created #8349345
meson-android
created #8349347
aarch64
meson-arm64
created #8349348
aarch64
meson-arm64-asan
created #8349349
aarch64
meson-arm64-build-test
created #8349346
aarch64
meson-armhf
created #8349350
meson-i386
created #8349353
meson-mingw32-x86_64
created #8349352
kvm
meson-ppc64el
created #8349351
kvm
meson-s390x