pan/bi: Decode all 32-bit register modes

There's actually more than 16 of them, disambiguated by `r2 == r3` and
`first?` as conditions for another "fun" encoding. The extra space
allows for writing half-registers.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6793>
3 files changed