Bind depth and stencil buffers separately.

Bug 27460431

Change-Id: Ice854b6faec09dc5f2cbdc2a5c3ffba9a73bfb70
Reviewed-on: https://swiftshader-review.googlesource.com/4977
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>