Implement texture enable. BUG=18110152 Change-Id: I47b38cb10ea0b73c522817f9dbe5a5d118f3c599 Reviewed-on: https://swiftshader-review.googlesource.com/1282 Reviewed-by: Nicolas Capens <nicolascapens@google.com> Tested-by: Nicolas Capens <nicolascapens@google.com>