util: Generalize fast integer division to be variable bit-width

util: Generalize fast integer division to be variable bit-width

There's nothing inherently fixed-width in the code.  All that's required
to generalize it is to make everything internally 64-bit and pass
UINT_BITS in as a parameter to util_compute_fast_[us]div_info.  With
that, it can now handle 8, 16, 32, and 64-bit integer division by a
constant.

We also add support for division by 1 and by other powers of 2.  This is
useful if you want to divide by a uniform value in a shader where you
have the opportunity to adjust the uniform on the CPU before passing it
in.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>