intel/compiler: Don't create vec4 reg-set for gen8+
After @idr's 60e1d0f0, we know that vec4 will never be used for gen > 8.
Cc: @currojerez, @idr
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After @idr's 60e1d0f0, we know that vec4 will never be used for gen > 8.
Cc: @currojerez, @idr