[regression][bisected] lowering passes from Zink break v3d alphatest test on piglit

After MR !2213 (merged) "lowering passes from Zink" landed on Master 44 piglit test related to Alpha Testing started to regress on V3D.

spec@arb_es2_compatibility@fbo-alphatest-formats
spec@arb_texture_float@fbo-alphatest-formats
spec@arb_texture_rg@fbo-alphatest-formats-float
spec@arb_texture_rg@fbo-alphatest-formats
spec@ext_packed_float@fbo-alphatest-formats
spec@ext_texture_srgb@fbo-alphatest-formats
spec@ext_framebuffer_object@fbo-alphatest-formats

The bisections points the following commit by @kusma

commit 9d0523b569bb7208c6e74cafc0f3945415d94336 (refs/bisect/bad)
Author: Erik Faye-Lund <erik.faye-lund@collabora.com>
Date:   Mon Oct 7 12:18:09 2019 +0200

    v3d: do not report alpha-test as supported
    
    This triggers lowering in the state-tracker, which makes things a bit
    simpler.
    
    Reviewed-by: Marek Olšák <marek.olsak@amd.com>

Probably this is affecting also to vc4, but needs to be confirmed.