util/format: expose generated format packing functions through a header

util/format: expose generated format packing functions through a header

Some of the generated functions can be useful without going through the
format table (filling border color struct in turnip). By not calling these
functions through the format table, we should eventually be able to garbage
collect the unused packing functions, and also allows LTOs to happen.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6093>