freedreno/ir3: Set the FS .msaa flag to true during precompiles.

If you're going out of your way to do per-sample interpolation, you are
almost surely going to be doing so to an MSAA framebuffer.  Should reduce
recompiles with MSAA enabled.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4562>

src/gallium/drivers/freedreno/ir3/ir3_gallium.c

@@ -152,6 +152,7 @@ ir3_shader_create(struct ir3_compiler *compiler,
 	 */
 	struct ir3_shader_key key = {
 		.tessellation = IR3_TESS_NONE,
+		.msaa = true,
 	};
 
 	switch (nir->info.stage) {