gallium: Add a uif() helper function to complement fui()

gallium: Add a uif() helper function to complement fui()

I found myself often wanting this when I'm printing out a uint32_t mapping
of some GPU data, and I want to put in an interpretation of that value as
a float.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>