Add low level uart debug support for imx7d
Signed-off-by: Frank Li <Frank.Li@freescale.com>
Signed-off-by: Bai Ping <b51503@freescale.com>
Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>