util: Explicitly call the unpack functions from inside bptc pack/unpack.

util: Explicitly call the unpack functions from inside bptc pack/unpack.

We were calling the table-based unpack functions from inside the pack and
unpack table's methods, so if anything included these pack functions (such
as a call to a table-based pack function), you'd pull in all of unpack as
well.

By calling them explicitly, we save some overhead in these functions
(switch statement, address math on the zero x,y arguments) anyway.

Reviewed-by: Jonathan Marek <jonathan@marek.ca>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6307>