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