freedreno/a3xx/compiler: handle kill properly (new compiler)

freedreno/a3xx/compiler: handle kill properly (new compiler)

Since 'kill' does not produce a result, the new compiler was happily
optimizing them out.  We need to instead track 'kill's similar to
outputs.  But since there is no non-predicated kill instruction,
(and for flattend if/else we do want them to be predicated), we need
to track the topmost branch condition on the stack and use that as src
arg to the kill.  For a kill at the topmost level, we have to generate
an immediate 1.0 to feed into the cmps.f for setting the predicate
register.

Signed-off-by: Rob Clark <robclark@freedesktop.org>