turnip: Tell spirv_to_nir that we want fragcoord as a sysval.

Fixes ir3 compiler failure failure in
dEQP-VK.renderpass.dedicated_allocation.formats.r8g8b8a8_unorm.clear.clear_draw
(now just a rendering failure where the subpass clear isn't happening)

Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>

src/freedreno/vulkan/tu_shader.c

@@ -38,6 +38,7 @@ tu_spirv_to_nir(struct ir3_compiler *compiler,
 {
    /* TODO these are made-up */
    const struct spirv_to_nir_options spirv_options = {
+      .frag_coord_is_sysval = true,
       .lower_ubo_ssbo_access_to_offsets = true,
       .caps = { false },
    };