translate: improve sse2 32-bit unsigned -> float conversion

translate: improve sse2 32-bit unsigned -> float conversion

The existing logic would drop the low bit. Instead, let's drop the high
bit, do the conversion, and then add the fixed constant back in if the
value had the high bit set originally.

Fixes KHR-GL45.direct_state_access.vertex_arrays_attribute_format on
drivers that use this module to handle the format conversion.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Acked-by: Emma Anholt <emma@anholt.net>
Tested-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14922>