iris: Fix ALT mode regressions from shader cache

iris: Fix ALT mode regressions from shader cache

We were checking this based on nir->info.name, but with the shader
cache enabled, nir_strip throws out the name, causing us to use IEEE
mode for ARB programs.

gl-1.0-spot-light regressed because it wants ALT mode for 0^0 behavior.

Fixes: dc5dc727d59 iris: Serialize the NIR to a blob we can use for shader cache purposes.