vrend: emit OES_shader_io_blocks for GLES 3.1 shaders with io blocks

While adding support to llvmpipe for GL 4.00 a bunch of virgl tests
started to fail, this should fix one of the cases

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

src/vrend_shader.c

@@ -5315,6 +5315,9 @@ static void emit_header(struct dump_ctx *ctx)
       }
 
       if (ctx->cfg->glsl_version < 320) {
+         if (prefer_generic_io_block(ctx, io_in) || prefer_generic_io_block(ctx, io_out)) {
+            emit_ext(ctx, "OES_shader_io_blocks", "require");
+         }
          if (ctx->shader_req_bits & SHADER_REQ_SAMPLE_SHADING)
             emit_ext(ctx, "OES_sample_variables", "require");
          if (ctx->shader_req_bits & SHADER_REQ_GPU_SHADER5) {