[igt-dev] [PATCH i-g-t] tests/kms_hdr: Fix failure to read output_bpc on AMD hardware

[Simon Ser]

I don't think removing TEST_ONLY is correct? bafd90661c26 ("tests/kms_hdr: Add
bpc switch subtests") reads:

    v4: -Plane size back to CRTC size, regression observed in hsw again
         "Plane must cover entire CRTC" because of plane size restriction
         to 512x512. Petri/Ville suggested to use TEST_ONLY in try_commit()
         to probe whether we can use a smaller than fullscreen plane.

cc Nicholas