agx: Fix accounting for phis

agx: Fix accounting for phis

All affected shaders are in pubg. Presumably, with the new demand calculation,
RA is hitting a higher target thread count at the expense of a little more live
range splitting.

   total instructions in shared programs: 1773295 -> 1773310 (<.01%)
   instructions in affected programs: 6058 -> 6073 (0.25%)
   helped: 0
   HURT: 15
   Instructions are HURT.

   total bytes in shared programs: 11695360 -> 11695450 (<.01%)
   bytes in affected programs: 40496 -> 40586 (0.22%)
   helped: 0
   HURT: 15
   Bytes are HURT.

   total halfregs in shared programs: 530844 -> 530724 (-0.02%)
   halfregs in affected programs: 1785 -> 1665 (-6.72%)
   helped: 15
   HURT: 0
   Halfregs are helped.

   total threads in shared programs: 18909440 -> 18910400 (<.01%)
   threads in affected programs: 12480 -> 13440 (7.69%)
   helped: 15
   HURT: 0
   Threads are helped.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24635>