Fix I2C dependency check for CFG_RTC

Signed-off-by: Petr Štetiar <ynezz@true.cz>
Add missing UART header if UART is enabled

Signed-off-by: Petr Štetiar <ynezz@true.cz>
lpc1347ref board testing

Signed-off-by: Petr Štetiar <ynezz@true.cz>