nir: add a high precision conversion unorm->float

We'll use this for D32->D24X8 conversion on Intel on Gfx11/Gfx12.0/DG2
(where HW doesn't have fp64 support).

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33422>
2 files changed