anv: don't advertise vk conformance on GPUs that aren't conformant

This sets the conformance version to 0.0.0.0 for GPUs that have
incomplete support for vulkan, so that it's easier to check if vulkan is
fully supported by a GPU at runtime for applications/libraries.

    $ vulkaninfo|grep conf
    MESA-INTEL: warning: Ivy Bridge Vulkan support is incomplete
        conformanceVersion = 0.0.0.0

Signed-off-by: Clayton Craft <clayton@craftyguy.net>
Reviewed-by: Ivan Briano <ivan.briano@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13275>

src/intel/vulkan/anv_private.h

@@ -880,6 +880,8 @@ struct anv_physical_device {
     struct brw_compiler *                       compiler;
     struct isl_device                           isl_dev;
     struct intel_perf_config *                    perf;
+   /* True if hardware support is incomplete/alpha */
+    bool                                        is_alpha;
     /*
      * Number of commands required to implement a performance query begin +
      * end.