agx: Only emit the used components of gl_FragCoord

In case a shader only use gl_FragCoord.xy, this avoids wasting
coefficient registers for gl_FragCoord.zw which should be a small
optimization. It's also less work for DCE but I'm less worried about
that.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17198>
1 file changed