pan/midgard: Optimize varying projection

pan/midgard: Optimize varying projection

We add a new opt pass fusing perspective projection with varyings. Minor
win..? We don't combine non-varying projections, since if we're too
agressive, the extra load/store traffic will hurt us so it's not really
a win in practice.

total instructions in shared programs: 3915 -> 3913 (-0.05%)
instructions in affected programs: 76 -> 74 (-2.63%)
helped: 1
HURT: 0

total bundles in shared programs: 2520 -> 2519 (-0.04%)
bundles in affected programs: 46 -> 45 (-2.17%)
helped: 1
HURT: 0

total quadwords in shared programs: 4027 -> 4025 (-0.05%)
quadwords in affected programs: 80 -> 78 (-2.50%)
helped: 1
HURT: 0

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>