pan/bi: Assign registers to ports

pan/bi: Assign registers to ports

Now that we can pack registers given the assigned ports, and we can
assign registers from the indices, the missing link is assigning ports
from the registers, and now finally we get some real data showing up in
a disassembly exercising lots of different code paths.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4242>