Different boards may use differenct UART ports for debugging.
To be able to add different debug UART configurations (e.g. UART2),
rename the existing general DEBUG_IMX6Q_UART to DEBUG_IMX6Q_UART4.
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>