util: Merge util_format_read_4* functions.

Everyone wants the same thing: unpack 4-bytes-per-channel data based on the
base type of the format.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5728>
5 files changed