radv: add RADV_DEBUG=novrsflatshading option

To easily debug if enabling VRS for flat shading is broken.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9515>

src/amd/vulkan/radv_pipeline.c

@@ -5312,6 +5312,10 @@ static bool
 gfx103_pipeline_vrs_coarse_shading(const struct radv_pipeline *pipeline)
 {
 	struct radv_shader_variant *ps = pipeline->shaders[MESA_SHADER_FRAGMENT];
+	struct radv_device *device = pipeline->device;
+
+	if (device->instance->debug_flags & RADV_DEBUG_NO_VRS_FLAT_SHADING)
+		return false;
 
 	if (!ps->info.ps.allow_flat_shading)
 		return false;