Add new compatible string for i.MX6UL SOC.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>