pan/bi: Unwrap BRANCH into CONDITIONAL class

We can simplify the IR considerably and unify more conditions, which
gives conditional discard for free.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4883>
4 files changed