svga: fix buffer binding flags initialization

If a buffer is created/initialized with glNamedBufferData we will
have no target (GL_ARRAY_BUFFER, GL_UNIFORM_BUFFER, etc) so the
svga_buffer::bind_flags will be zero until we try to get the buffer
handle.

This patch initializes the svga_buffer::bind_flags field when it's
zero.

This fixes the Piglit arb_uniform_buffer_object-rendering-dsa test.

Note that there's still issues in this area that'll have to be
addressed in the future.  For example, creating a buffer object
as GL_UNIFORM_BUFFER and later using it as a vertex buffer will
fail.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>

src/gallium/drivers/svga/svga_resource_buffer_upload.c

@@ -1003,6 +1003,12 @@ svga_buffer_handle(struct svga_context *svga, struct pipe_resource *buf,
             return NULL;
       }
    } else {
+      if (!sbuf->bind_flags) {
+         sbuf->bind_flags = tobind_flags;
+      }
+
+      assert((sbuf->bind_flags & tobind_flags) == tobind_flags);
+
       /* This call will set sbuf->handle */
       if (svga_have_gb_objects(svga)) {
          ret = svga_buffer_update_hw(svga, sbuf, sbuf->bind_flags);