agx: Fuse conditions into if's

agx: Fuse conditions into if's

Simple greedy thing that has the potential to inflate register pressure but
reduces instructions. Thanks to the recent loop work that turns if { break }
into while_icmp, this also implicitly handles fusing conditions into loops,
which is what actually prompted this.

Surprisingly, this helps register pressure on my shader-db (no change to thread
count), I guess by eliminating the boolean temps in case where the sources are
used multiple times.

   total instructions in shared programs: 1786561 -> 1784943 (-0.09%)
   instructions in affected programs: 128557 -> 126939 (-1.26%)
   helped: 474
   HURT: 13
   Instructions are helped.

   total bytes in shared programs: 11733236 -> 11720734 (-0.11%)
   bytes in affected programs: 976034 -> 963532 (-1.28%)
   helped: 521
   HURT: 13
   Bytes are helped.

   total halfregs in shared programs: 474245 -> 474094 (-0.03%)
   halfregs in affected programs: 1869 -> 1718 (-8.08%)
   helped: 28
   HURT: 7
   Halfregs are helped.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25052>